Electrically conductive liquids based on metal-diphosphonate complexes

ABSTRACT

The invention relates to electrically conducting liquids based on diphosphonate complexes and to the use thereof in methods for electrolytically modifying the surface of a flat metal workpiece. The invention further relates to the flat metal workpieces produced by said method and to the use of the metal workpieces as a substrate for forming permanent adhesive bonds with a plurality of materials and for accommodating liquid and solid materials.

The present invention relates to electrically conductive liquids based on diphosphonate complexes and the use thereof in methods for the electrolytic surface modification of a flat metal workpiece. The invention furthermore relates to the flat metal workpieces produced with this method and to the use of the metal workpieces as substrate for the formation of strong adhesive bonds with a plurality of materials and for the accommodation of liquid and solid materials.

The electrolytic coating of a metal surface with a metal or a metal alloy represents a known method for the surface treatment of a metal workpiece, such as for example a metal strip or a sheet. For example, in the case of electrolytic strip coating, the strip is guided through one or more electrolytic cells. In each electrolytic cell, the strip is usually brought into a solid-solid connection with the negative terminal of a rectifier via so-called current rolls. The strip consequently serves as negative electrode, i.e. as cathode. As a rule, the positive electrode, i.e. the anode, is formed as a pair of electrodes, wherein the strip runs through between the two electrodes.

Disadvantages in this method manifest themselves in particular in the transition from higher strip thicknesses to foil thicknesses, in that considerable difficulties and limitations can occur to the extent that (a) the foil overheats and oxidizes due to the waste heat of the current conduction from the current roll, as a result of which the required currents can no longer be achieved, (b) due to the low effective cross-section of a foil the inner resistance becomes very high, as a result of which overheating of the foil between the current roll and the electrolyte surface and oxidation damage may occur, (c) on contact of the foil with the current roll local resistance peaks occur due to tiny particles and residues which have not been removed, which can lead to penetration welding or local discoloration of the foil, and (d) due to the pre-treatment used and the subsequent running of the foil in the coating installation the activation of the surface of the foil remains limited to reduction and superficial etching of the grain boundaries, with the result that no structurally optimized surface is present for the subsequent electrolytic deposition of metal.

Through the electrolytic coating, the metal workpiece to be coated is provided with a substantially level metal coating uniformly on all sides. Even if metal workpieces having a relatively rough surface nature are used, the surface is levelled. However, for applications in which good adhesion to another material is required, a smooth surface may be undesirable. Good adhesion between two materials is achieved when there is a chemical interaction and/or a mechanical engagement in topographical features of the adhesion partners. If this is not or not sufficiently the case, the adhesion deteriorates. Thus, poor adhesion between a metal surface and the same or a different material, for example a lacquer layer, a paint layer or an adhesive, can lead to products which are of inferior quality or even unusable.

Various technical solutions have been developed to improve the adhesion to metal surfaces. Anodizing is known as an electrolytic process for improving adhesion to metal surfaces. In the case of anodizing a regularly structured, porous oxide layer is formed on the surface of a metal workpiece connected as anode using an acidic electrolyte, such as e.g. sulphuric, phosphoric or chromic acid. The pores enable the mechanical engagement of the anodized metal workpiece with another material, such as a paint, lacquer or adhesive layer. However, anodizing is limited to a few metal workpieces, such as, for example, aluminium, titanium and alloys. Above all, anodizing aluminium is industrially significant (Eloxal process; electrolytic oxidation of aluminium). Here, an aluminium oxide layer with a porous structure forms on the surface of the aluminium material.

A solution to the problems emerging in the conventional methods described or the combination thereof is the neutral conductor principle (NCP), which is used in the electrolytic cleaning and the electrolytic etching of continuous material (strip, wire). In this procedural principle a combined anodic and cathodic treatment takes place. During the anodic treatment an erosion process is induced, in which tiny particles and residues or impurities located on the surface of the metal foil are removed and a bright surface is obtained. In the subsequent cathodic treatment a deposition/coating process is induced, in which a metal is deposited out of the treatment liquid onto the cleaned and bright surface. In the closed NCP the same treatment liquid is used for the region of the cathodically poled electrode and for the region of the anodically poled electrode, i.e. for the erosion and the coating step. In the open NCP (with separate baths) two different treatment liquids, which are not in contact with each other, are used.

The serious disadvantage of the closed neutral conductor principle compared with conventional galvanic coating with solid-solid contact is that the erosion of the surface of a substrate and the subsequent coating of the substrate with a foreign material cannot be realized with a permanently constant quality and composition of the treatment liquid. Although in the open neutral conductor principle this disadvantage is eliminated by using different treatment liquids, changing the treatment liquid involves other disadvantages inasmuch as the contact of the substrate with the liquid, for example in an intermediate rinse, is interrupted and the non-wetted regions of the substrate are exposed to the atmosphere after the electrolytic erosion. Due to the passivation which thereby starts and, where appropriate, recorrosion of the freshly opened surface, the actual advantage of the neutral conductor principle is limited again or forfeited. Furthermore, cooling of the substrate is interrupted by the treatment liquid.

Proposed solutions, for example by encapsulating the electrode chamber of the erosion zone with ion-specific membranes, as described, for example, in DE 199 51 324, in their turn have disadvantages since (i) entrainment of the dissolved metal ions in the running direction of the continuous material is not prevented, (ii) for the ion-specific membrane for a technically usable ion separation large differences in the properties or concentrations of the ions to be separated generally have to be present, (iii) in an ion exchange action of these membranes redox processes between the ions are not suppressed and (iv) the continuity of the overall process no longer exists due to the exhaustion of the exchanger capacity of the membrane.

In addition to conventional metal salt electrolytes of metal ions and simple anions, such as, for example, aqueous metal sulphate solutions, inter alia metal complexes of metal ions and ligands or complexing agents from the family of polyhydroxycarboxylic acids, polyamino-, -imino- or -nitriloacetic acids, -methylenephosphonic acids and -3-propionic acids and mixtures thereof are used as electrolytes for the deposition of metal surfaces in galvanic coating methods. The use of complexing agents serves to improve the deposition method and is essential for achieving adequate solubility and stabilising of selected oxidation states of metal ions in particular pH ranges (conventionally 3.5<pH<11.5). Polyhydroxycarboxylic acids, polyamino-, -imino- and -nitriloacetic acids, methylenephosphonic acids and -3-propionic acids, and mixtures thereof are not sufficiently stable in the electrolytic process since they are subject to destruction in the Kolbe electroreaction or decompose in a secondary reaction after the oxidation of the methylene, amino, imino or nitrilo function. Carboxylates are thus oxidized to carboxyl radicals at the anode, which stabilize into a highly reactive alkyl radical by splitting off carbon dioxide. These radicals start further bond cleavages, and as a rule this leads to conversion of the constituents mentioned into carbonate and poorly soluble decomposition products, which have to be removed constantly from the process. Methylenephosphonates, which in practice are derivatives of formaldehyde, behave similarly. This methylene group is likewise readily oxidized with the formation of formate or carbonate, as a result of which the N-methylene bond and the P-methylene bond break. The decomposition products, which as a rule are amines, hydroxylamines and phosphates and are very difficult to remove, then accumulate in the electrolyte.

DE 3347593 describes electrolytes, which comprise copper complexes of copper ions and a diphosphonate ion as a complexing agent and a buffer, for conventional galvanic coatings. The diphosphonate-based electrolytes described therein are preferably prepared from copper(II) sulphate and used at elevated bath temperature for deposition of a copper layer. The diphosphonate electrolytes of DE 3347593 prove to be unsuitable for use in methods for surface modification according to the neutral conductor principle because of their sulphate content. Hard anions, such as sulphate or chloride, are suitable for breaking the passivation of the anode surface and for rendering possible an anodic erosion reaction, but in the method according to the neutral conductor principle they prove to be a disadvantage, especially in combination with the diphosphonate ion, since at the anode they lead to the side reaction of creeping oxidation and destruction of the diphosphonate ion or of other organic control additives.

There is thus a need for an improved electrolyte or for an improved method for the electrolytic surface modification of flat workpieces. It is therefore the object of the present invention to provide an improved treatment liquid for an improved method for the modification of a metal surface of a flat metal workpiece without the existing disadvantages of the state of the art. A constituent of this need is to establish an electrolyte family which shows almost the same surface activity independently of the metal to be eroded and of the metal to be deposited and which is capable, due to the familial similarity, of preparing the surface in the erosion step in an optimum manner for the subsequent deposition. The electrolyte family should have a density which varies within narrow limits and a pH which varies within narrow limits, and apart from the metal ions to be eroded or to be deposited should consist of identical components, not be acid and be of high ionic strength. Under these prerequisites, for example, the separation of the erosion and deposition zone in the NCP by an immiscible, non-conducting, heavy, inert separating liquid becomes realistic, and the substrate can be eroded and coated with elements foreign to the substrate with continuous wetting and cooling in the NCP.

With the aid of this improved treatment liquid or this improved method, it should be possible for metal surfaces to be modified by application of aggregates of one or more different metals distributed uniformly over the area, in order for example to provide flat metal workpieces having an improved adhesive strength on coatings applied to the metal workpieces.

A further object of the present invention is to provide treatment liquids with which it is possible to deposit on flat metal workpieces coatings with metal ions which hitherto could not be deposited in electrolytic methods as a treatment on metal surfaces.

BRIEF DESCRIPTION OF THE INVENTION

To achieve the abovementioned objects, according to the invention an electrically conductive liquid comprising an aqueous solution of a metal complex is provided, wherein the metal complex is a complex of

-   -   (i) one or more metals selected from the group consisting of Cu,         Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co, Ti, Zr, Nb, Y, Nd, Sm, Gd,         Tb, Dy, Ho, Er, Tm, Yb, Lu or mixtures thereof, and     -   (ii) one or more diphosphonate ligands of the general formula         (I)

O═P(OH)₂—X—(OH)₂P═O  (I)

-   -   -   wherein the OH groups in the general formula (I) which are             bonded to the two phosphorus atoms independently of each             other are protonated (OH) or deprotonated (O⁻),         -   wherein:         -   X=O, NR¹ or CR¹R², in particular X=CR¹R², wherein             -   R¹=H, C₁-C₁₈-n-alkyl or C₃-C₁₈-isoalkyl,                 C₅-C₆-cycloalkyl, unsubstituted or substituted benzyl                 and substituted or unsubstituted phenyl,         -   R²=R¹, —OR³ or —NHR³, and         -   R³=H, C₁-C₄-n-alkyl or C₃-C₄-isoalkyl, and             wherein the liquid furthermore optionally comprises an             additive of the general formula (II):

R¹⁰—CHR⁸—CHR⁹—Z—(CHR⁴—CHR⁵—Z)_(n)—CHR⁶—CHR⁷—R¹⁰  (II)

wherein:

-   -   n=an integer from 1 to 11, in particular an integer from 1 to 3,     -   Z=S or O, in particular S,     -   R⁴=H, C₁₋₄-alkyl or phenyl,     -   R⁵=H, C₁₋₄-alkyl or phenyl,     -   R⁶=H, C₁₋₄-alkyl or phenyl,     -   R⁷=H, C₁₋₄-alkyl or phenyl,     -   R⁸=H, C₁₋₄-alkyl or phenyl,     -   R⁹=H, C₁₋₄-alkyl or phenyl,     -   R¹⁰=OH, COOH or COOR¹¹ and     -   R¹¹=alkyl (in particular C₁₋₄-alkyl), Li, Na or K.

If the metal is Cu, in the present invention the additive is preferably present in an amount of from 0.05 to 0.5 wt. %, more preferably in an amount of from 0.1 to 0.2 wt. %.

This electrically conductive liquid forms the treatment liquid (electrolyte) for a method according to the invention for the electrolytic surface modification of a flat metal workpiece in which at least one surface of the flat metal workpiece is anodically polarized in a treatment liquid and an anodic dissolving process is thereby induced, and the at least one surface of the flat metal workpiece is then cathodically polarized in a treatment liquid from the same group of treatment liquids and a cathodic deposition process is thereby induced for the deposition of one or more metals on the at least one surface of the flat metal workpiece. The method according to the invention renders possible the production of flat metal workpieces which are modified in the surface and which according to a further aspect of the invention can serve as substrate for the formation of strong adhesive bonds with other materials.

DETAILED DESCRIPTION OF THE INVENTION

The electrically conductive liquid of the present invention which is used as the treatment liquid in the method according to the invention for the electrolytic surface modification of a flat metal workpiece comprises an aqueous solution of a metal complex. Specifically, the metal complex is the complex of a metal with ligands of the formula (I), wherein the metal can be either a single or two or more different metals.

The metal or the several metals of the metal complex are selected from the group consisting of Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co, Ti, Zr, Nb, Y, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or mixtures thereof. Preferably, the metal is selected from Cu, Zn, Mn, In, Sn, Sb, Bi, Co, Ti, Zr, Nb and mixtures thereof. Particularly preferably, the metal is selected from Mn, Cu, Zn, Cd, In, Sn, Sb, Bi and mixtures thereof, in particular Cu, Zn, Sn, Bi and mixtures thereof. Specifically, the metal of the metal complex is Cu, Sn, Sb or a mixture thereof. If more than one metal is present, it is preferably a combination of Zn and Cu or Ni and Cu. In further preferred embodiments the metal is selected from Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co and mixtures thereof and is doped with one or more doping metals. Suitable doping metals in the present invention are Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ti, Zr, Nb and mixtures thereof. Preferred combinations of metal and doping metal are combinations of Sn and Gd; Sn and Zr; Zn and Y, Dy, Zr or mixtures thereof, or combinations of Fe, Ni, Co or mixtures thereof with Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or mixtures thereof, such as, for example, Ni, Gd and Tb; Fe and Ln (Ln=Sm, Gd, Dy, Er); Co and Ln (Ln=Nd, Sm, Gd, Dy, Er).

Suitable diphosphonate ligands are compounds of the general formula (I)

O═P(OH)₂—X—(OH)₂P═O  (I)

wherein: X=O, NR¹ or CR¹R², wherein R¹=H, C₁-C₁₈-n-alkyl or C₃-C₁₈-isoalkyl, C₅-C₆-cycloalkyl, unsubstituted or substituted benzyl and substituted or unsubstituted phenyl, R²=R¹, —OR³ or —NHR³, and R³=H, C₁-C₄-n-alkyl or C₃-C₄-isoalkyl.

The OH groups in the general formula (I) which are bonded to the two phosphorus atoms independently of each other are present in the protonated (OH) or deprotonated (O⁻) form.

Preferably, in the general formula (I) X=CR¹R².

Preferably, 2, 3 or 4 (all) of the hydroxyl groups of the diphosphonate ligand of the general formula (I) which are bonded to the two phosphorus atoms are deprotonated. Diphosphonate ligands of the general formula (I) which are deprotonated in this way can be used in the pH range between about 6.5 and 11.0.

Depending on the specific combination of metal(s) and diphosphonate ligands, the molar ratio of metal:diphosphonate is preferably 1:2 to 1:4. The diphosphonate ligand can moreover form different chelates with the central ions, wherein as a rule it can add on in the bidentate or tridentate form. The size of the chelated ring ranges from 4 via 5 to 6.

Depending on the metal or the metals in the complex, various routes can be taken for the preparation of the electrically conductive liquids based on metal-diphosphonate complexes.

For example, oxides or carbonates of the desired metals are treated with the free diphosphonic acid. Neutralization, for example with potassium hydroxide solution, is then carried out to establish the optimum pH range, which as a rule is in the range of from 8.5 to 10. By this preparation method the introduction of hard ions, such as e.g. halides or sulphates, into the treatment liquid is to the greatest extent or completely avoided.

This method is preferably suitable for the preparation of the diphosphonate complexes of copper, of zinc, of manganese, of indium, of tin, of antimony, of bismuth, of yttrium of lanthanum and of the lanthanoids praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Diphosphonate complexes of cobalt are also accessible by this route, although the stability thereof at pH values between 8.5 and 10 is limited. The cobalt-diphosphonate complex is stable for up to 48 h in solution. In order to achieve a longer stability, however, it must preferably be blended with the diphosphonate complex of a lanthanoid(III) ion within 8 hours of being obtained.

Another route for the preparation of metal-diphosphonate liquids which are free from foreign anions is the electrolytic metallization of dipotassium-diphosphonate or of a diphosphonate complex of a so-called “inert” metal ion, i.e. ions which cannot be deposited as metals electrolytically from aqueous solution, with an excess of dipotassium-diphosphonate in a special electrolytic cell. This cell operates with a current density ratio between the anode and cathode of at least 1:10, and both electrodes consist of the metal to be incorporated into the liquid, or in deviation the cathode consists of titanium, high-grade steel, gold or platinum. The cathode can be provided with an electrode bag. The dipotassium salt or the complexes or mixtures thereof serve as the diphosphonate base component. The diphosphonate complexes of the trivalent ions of Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, which are easy to prepare, for example, from the corresponding metal oxides, 1-hydroxyethane-1,1-diphosphonic acid (HEDP) and potassium hydroxide, are preferably used.

By using the diphosphonate complexes of Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and/or Lu, it is also possible to obtain metal-diphosphonates which are stable at pH values of from 8.5 to 10, for example of cobalt, nickel or iron (as mixed metal-diphosphonates). This is surprising, since pure nickel- or iron-diphosphonate complexes do not exist in the range between pH=8.5 and pH=10, and pure cobalt-diphosphonate complexes are not stable. Mixed metal-diphosphonate complexes are accessible, for example, by joint treatment of suitable metal salts with free diphosphonic acid, by metallization of a Y- and/or Ln-diphosphonate or by blending metal-diphosphonate complexes with Y- and/or Ln-diphosphonate complexes, the latter often being called dilution complexes in this function. The individual diphosphonate-based solutions are conventionally miscible with each other in any ratio.

For example, for the preparation of the liquids containing iron-diphosphonate the electrolytic metallization of unsaturated lanthanoid-diphosphonate with iron(II) ions is the optimum route which can be taken for the preparation of a usable treatment liquid.

The nickel-diphosphonate electrolytes are best prepared by joint dissolving of lanthanoid(III) oxide and nickel(II) hydroxide or nickel(II) carbonate in HEDP and subsequent pH adjustment by means of potassium hydroxide solution, wherein the nickel content in comparison with the sum of all the complexing ions should never be more than 20 mol %.

Stable cobalt-diphosphonates can likewise be prepared by joint dissolving of lanthanoid(III) oxide and cobalt(II) carbonate in HEDP and subsequent pH adjustment by means of potassium hydroxide solution, wherein the cobalt content may be up to 85 mol % of the sum of all the complexing ions.

Titanium and zirconium are also called inert ions in the present invention, since they cannot be deposited as metals electrolytically from water. In the form of their oxides they have a considerable potential in corrosion protection and in the Cr(VI)-free passivation of metal surfaces. Their preparation and use therefore does not take place not with the aim of depositing Ti or Zr as metallic layers, but they are to be used instead of or with the lanthanoid complexes as an additive to the diphosphonate complexes or stabilizers of diphosphonate complexes of metals which can be deposited (e.g. Zn, Cu, Ni, Co, Fe, In, Sn, Sb, Bi). The corresponding diphosphonate complexes of these Ti(IV) or Zr(IV) ions are prepared via the solution of the acid sulphates, since HEDP is not acid enough to dissolve the basic carbonates or even oxides of these elements. The stable complex solutions have a maximum metal(IV)-diphosphonate ratio of 1:3. The mixture of the acid sulphates and the HEDP solution leads to precipitation of the HEDP, which is reversed by the rapid, extremely exothermic adjustment by means of potassium hydroxide solution. Directly after the dissolving of the HEDP the precipitation of well-crystallized potassium sulphate already starts due to the high potassium excess in the solution. By cooling the complex solution to temperatures of between 0° C. and 5° C. the solubility difference between the potassium sulphate and the remaining components leads to almost complete precipitation of the sulphate. The residual concentration of sulphate in these diphosphonate complexes of Ti(VI) and Zr(IV) is less than 1 g/l.

In order to reduce the sulphate concentration further, a barium-diphosphonate suspension is added, accompanied by stirring, to the solution obtained after the precipitated sulphate has been separated off (suspension: 1 part by weight of a 60 wt. % strength solution of diphosphonic acid in water and 1.84 parts by weight of barium hydroxide octahydrate). The precipitate formed is filtered off after 2 h. The sulphate concentration after this additional treatment method is about 1 mg/l.

The liquid which is electrically conductive according to the invention can comprise as a further component an additive of the general formula (II):

R¹⁰—CHR⁸—CHR⁶—Z—(CHR⁴—CHR⁵—Z)_(n)—CHR⁶—CHR⁷—R¹⁰  (II)

wherein:

-   -   n=an integer from 1 to 11, in particular an integer from 1 to 3,     -   Z=S or O, in particular S,     -   R⁴=H, C₁₋₄-alkyl or phenyl,     -   R⁵=H, C₁₋₄-alkyl or phenyl,     -   R⁶=H, C₁₋₄-alkyl or phenyl,     -   R⁷=H, C₁₋₄-alkyl or phenyl,     -   R⁸=H, C₁₋₄-alkyl or phenyl,     -   R⁹=H, C₁₋₄-alkyl or phenyl,     -   R¹⁹=OH, COOH or COOR¹¹ and     -   R¹¹=alkyl (in particular C₁₋₄-alkyl), Li, Na or K.

If the compound of the formula (II) comprises enantiomers or diastereomers, both the pure enantiomers or diastereomers and the corresponding mixtures can be used.

In particular, within the framework of the present invention C₁₋₄-alkyl is methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl or sec-butyl, preferably methyl, ethyl, n-propyl or n-butyl.

Preferably, in the additive of the formula (II):

-   -   n=an integer from 1 to 3,     -   Z=S,     -   R⁴=H, methyl, ethyl, n-propyl or n-butyl,     -   R⁵=H, methyl, ethyl, n-propyl or n-butyl,     -   R⁶=H, methyl, ethyl, n-propyl or n-butyl,     -   R⁷=H, methyl, ethyl, n-propyl or n-butyl,     -   R⁸=H, methyl, ethyl, n-propyl or n-butyl,     -   R⁹=H, methyl, ethyl, n-propyl or n-butyl,     -   R¹⁰=OH, COOH or COOR¹¹, and     -   R¹¹=K, methyl, ethyl or n-propyl.

Alternatively, the additive of the formula (II) is a compound of the formula (III):

HO—(CHR⁶—CHR⁷—Z)_(n)—CHR⁶—CHR⁷—OH  (III)

wherein:

-   -   n=an integer from 1 to 11,     -   Z=S or O,     -   R⁶=H, methyl or phenyl and     -   R⁷=H, methyl or phenyl,         wherein preferably n=1-3 and Z=S.

Particularly preferably, the additive is a compound of the formula (II) wherein

-   -   n=1 or 2, in particular 1,     -   Z=S,     -   R⁴=R⁵=H or methyl,     -   R⁶=R⁹=H or methyl,     -   R⁷=R⁸=H or methyl,     -   R¹⁰=OH, COOH or COOR¹¹ and     -   R¹¹=K, methyl, ethyl or n-propyl.

Still more preferably, the additive is a compound of the formula (IV):

R¹⁰—CHR⁵—CHR⁹—S—CH₂—CH₂—S—CHR⁶—CHR⁷—R¹⁰  (IV)

wherein

-   -   R⁶=R⁹=H or methyl,     -   R⁷=R⁸=H or methyl and     -   R¹⁰=OH, COOH or COOK.

A particularly preferred additive of the general formula (II) is 1,8-dihydroxy-3,6-dithiaoctane (DTO).

The additives of the formula (II) are commercially obtainable or can be obtained by known chemical synthesis methods or analogously to these.

The additive is conventionally present in the liquid according to the invention in an amount of from 0 to 1 wt. %, preferably in an amount of from 0.05 to 0.7 wt. %, particularly preferably in an amount of from 0.1 to 0.5 wt. %, based on the weight of the total solution. If the electrically conductive liquid comprises the copper-diphosphonate complex as the only metal-diphosphonate complex, it preferably comprises the additive in an amount of from 0.05 to 0.2 wt. %, based on the total solution. In one embodiment of the present invention the metal of the metal-diphosphonate complex is Cu and 1,8-dihydroxy-3,6-dithiaoctane is used as the additive. Preferably, in this embodiment the amount of additive is 0.05 to 0.2 wt. %, based on the total solution.

In a specific embodiment of the invention the electrically conductive liquid is substantially free from sulphate and halide ions. The designation “substantially free” in the context of this invention means a residual concentration of these ions of less than 45 ppm (weight) for halides and of less than 120 ppm (weight) for sulphate. In still a further specific embodiment the metal of the metal complex is selected from the group consisting of Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co, Nb and mixtures thereof and the electrically conductive liquid is substantially free from sulphate and halide ions.

In yet a further embodiment of the invention the liquid according to the invention comprises, in addition to the diphosphonate of the formula (I), no additional buffer, such as, for example, carbonates, borates, acetates or mixtures thereof.

The electrically conductive liquid of the present invention has specific properties which render it suitable in particular for use as a treatment liquid in methods for the electrolytic surface modification of metal substrates. For such methods, treatment liquids are required which are provided with components which are stable, for example, in an erosion process of the surface modification method, i.e. are not decomposed or are decomposed to only a small extent, and in a deposition process of the surface modification method engage in the electrical double layer by intervention into the processes via secondary equilibria and/or lead to the growth of sub-microaggregates, which are small, are crystalline and compact in themselves and are distributed uniformly over the area.

The present invention therefore also provides a method for the electrolytic surface modification of a flat metal workpiece in which at least one surface of the flat metal workpiece is anodically poled in a treatment liquid and an anodic dissolving process is thereby induced, and the at least one surface of the flat metal workpiece is then cathodically poled in a treatment liquid and a cathodic deposition process is thereby induced for the deposition of one or more metals on the at least one surface of the flat metal workpiece, wherein one or more of the electrically conductive liquids described above is used as the treatment liquid.

The use of the treatment liquids based on metal-diphosphonate complexes in the method according to the invention for the electrolytic surface modification can take place in diverse embodiments.

In one embodiment of the deposition process of the method according to the invention, which follows the principle of conventional strip galvanizing, the strip as the substrate is connected as cathode via a solid-solid contact lying outside the treatment liquid in the form of a current roll. The anode is arranged parallel to the strip surface opposite one or both sides of the strip. In this form of the deposition process the diphosphonate complexes deliver an advantageous contribution in particular if only acid, highly alkaline or cyanidic electrolytes of the metals to be deposited are otherwise available, or if the diphosphonate complexes of several metals in a treatment liquid otherwise cannot be obtained in this combination. These include inter alia the treatment solutions based on the diphosphonate complexes of the monometals Sn, Zn, Sb, In, Bi and Cu (in combination with DTO), and the bi- and trimetals: Sn—Gd-DTO, Sn—Zr, Zn—Zr, Fe-Ln, Co-Ln and Ni-Ln. The use of these treatment liquids remains limited here only to low current densities (as a rule <8 A/dm²), since on dissolving of the layer into individual aggregates using higher current densities the adhesive strength decreases constantly with increasing current density due to the inadequately prepared surface.

In a further embodiment of the method according to the invention for the electrolytic surface modification of a flat metal workpiece according to the closed neutral conductor principle the flat metal workpiece is brought into solid-solid contact neither cathodically nor anodically, but is anodically polarized (positively) by at least one cathode and then cathodically polarized (negatively) by at least one anode. The current is transferred to the flat metal workpiece not by direct contacting of the flat metal workpiece via a contact element (such as e.g. a current roll in the case of strip galvanizing) connected to a current source, but through the treatment liquid. During the anodic polarization an anodic dissolving or erosion process is induced on a surface of the flat metal workpiece, in which tiny particles and residues or impurities located on the surface of the metal foil are removed, whereby a metallically bright surface is obtained. Furthermore, the topographical features of the metal surface, in particular the roughness peaks, are levelled. Furthermore, the anodic polarization or the anodic dissolving process thereby induced leads to an activated surface for the subsequent metal deposition. In particular, the surface obtained with the method according to the invention exhibits structural similarity or structural identity with the metal aggregates deposited on the surface of the flat metal workpiece in the subsequent deposition process (epitaxy or syntaxy). Through the cathodic polarization which follows, a cathodic deposition process is induced, in which a metal or a metal alloy (i.e. several different metals) is deposited on the surface of the flat metal workpiece.

In a specific embodiment according to the open neutral conductor principle (NCP) erosion and deposition take place in separate cells, which are present advantageously separated by a blow off zone, a rinse or both in combination, in order to prevent entrainment of the treatment liquid of the erosion reaction (anode) into the treatment liquid of the deposition reaction (cathode).

For the erosion reaction a treatment liquid is then advantageously used which is based on diphosphonate and comprises the same metal as the substrate and which consists only of a mixture of potassiumdihydrogen- and potassium-hydrogen-diphosphonate (K₂H₂Cb and K₃HCb) or of a diphosphonate complex of one or more inert metal ions, preferably the complexes of Y, Nd, Sm, Gd to Lu, Zr, with an excess of the potassium salts of the ligand, preferably K₂H₂Cb, K₃HCb and K₄Cb (wherein H₄Cb is the abbreviation of (tetravalent/tetraproton) diphosphonic acid). This embodiment can be transferred seamlessly to the treatment of a discrete flat metal workpiece in the appropriately cyclic method. This embodiment already allows the use of high current densities in order to deposit firmly adhering individual aggregates. It can be operated at current densities of up to 27 A/dm². As the current density increases, the layer deposited in compact form changes into individual aggregates, which are very firmly adhering. Conventional galvanizing cannot present such individual aggregates in a firmly adhering form.

This embodiment is of such interest since existing installations can be used for this by converting the etching by incorporation of the auxiliary cathodes into the erosion cell and retaining the conventional deposition by exchanging the current rolls for guide rollers while retaining the anodes as the deposition zone in the open neutral conductor principle.

The passivation of the freshly eroded surface by the atmosphere or the rinsing water is visibly suppressed, in contrast to acid treatment liquids, by the diphosphonate itself or, for example, by DTO or by both (if DTO is present as an additive) and the activity of the surface is adequately obtained.

The flat metal workpiece used within the framework of the present invention is preferably a metal workpiece with a thickness which is at least 100 times, more preferably at least 1,000 times and particularly preferably at least 10,000 times smaller than the length and/or width of the metal workpiece. Consequently, as a rule, the term “surface of the flat metal workpiece” means the area defined by the length and width, not the area defined by the thickness and width or thickness and length. The flat metal workpiece is preferably a metal strip or a metal foil. The term “metal strip” herein refers to a flat metal workpiece with a given width and a thickness of from 100 μm to 1 mm. The term “metal foil” refers to a flat metal workpiece with a given width and a thickness of less than 100 μm, conventionally with a thickness of from 2 μm to less than 100 μm.

As a rule, the flat metal workpiece consists entirely of a single metal, in particular of copper, tin, zinc, aluminium, iron, nickel. However, it can also consist of a metal alloy, for example of at least two of the named metals, preferably of a copper wrought alloy, iron alloy, silver alloy or tin alloy. A flat metal workpiece made of steel can also be used. Particularly preferably, the flat metal workpiece is a copper foil, a copper strip, a tin-plated foil or a tin-plated strip, in particular a tin-plated copper foil or a tin-plated copper strip.

Furthermore, the flat metal workpiece can also consist of two or more layers of a metal or a metal alloy, wherein the layers can be the same or different. Furthermore, the flat metal workpiece can be formed in such a way that at least one and preferably both surfaces of the flat metal workpiece consist of a metal or a metal alloy and the remaining part of the flat metal workpiece can be made of any material, as long as this is suitable for use in the method according to the invention.

Before use in the method according to the invention, the flat metal workpiece is usually pre-treated. Appropriate pre-treatment methods are known in the state of the art and comprise, for example, degreasing, rinsing with water, aqueous surfactant solutions or solvents and pickling with the solution of a mineral acid in water, preferably sulphuric acid.

During the electrolysis, the flat metal workpiece is preferably guided through the treatment liquid and past the at least one cathode and the at least one anode. This is carried out in such a way that the described anodic polarization and cathodic polarization and the anodic dissolving process and cathodic deposition process thereby induced take place. In the case of continuous metal foils or strips these are usually guided through the treatment liquid using guiding elements (e.g. guide rollers). If a continuous foil installation is used to carry out the method according to the invention, several electrolysis baths (electrolytic cells) can also be connected in series.

Within the framework of the present invention, a variety of arrangements of the at least one cathode and the at least one anode are conceivable. For example, 1, 2, 3, 4 or more cathodes and 1, 2, 3, 4 or more anodes can be used per electrolytic cell or electrolyte bath. This can be arranged differently (e.g. alternately cathode and anode, first all cathodes and then all anodes, several cathodes alternating with several anodes, cathodes and anodes arranged only on one side of the flat metal workpiece or on both sides etc.).

According to a preferred embodiment, at least one cathode pair and at least one anode pair are preferably used. The two cathodes of the cathode pair and the two anodes of the anode pair are arranged on opposite sides of the flat metal workpiece, such that the flat metal workpiece is located between the two anodes and between the two cathodes. Anodic or cathodic polarization consequently occurs on both sides of the flat metal workpiece. Such a configuration permits the two-sided modification of the flat metal workpiece with deposited metal aggregates. According to another preferred embodiment, the flat metal workpiece is first of all anodically polarized by two cathodes which are arranged on the same side of the flat metal workpiece and then cathodically polarized by two anodes which are both arranged on the same side of the flat metal workpiece as the cathodes.

Usually, the at least one surface of the flat metal workpiece is first anodically polarized by the at least one cathode and then cathodically polarized by the at least one anode. However, it is also provided that the cycle “anodic polarization/cathodic polarization” is run through several times. Furthermore, the flat metal workpiece can be polarized one or more times anodically and one or more times cathodically in any sequence, wherein typically the anodic dissolving process predominates first and then the cathodic deposition process predominates. A phase with a dominating dissolving process can be interrupted by a short phase with the deposition process (dominating dissolving process, interrupted by deposition process) and vice versa (dominating deposition process, interrupted by dissolving process). The one or more anodic polarizations and the one or more cathodic polarizations can, as already mentioned above, be achieved using a corresponding number of spatially separated anodes and cathodes. However, it is also possible to use electrodes which are connected (contacted) optionally positively or negatively and consequently function both as cathode and as anode.

The cathodes and anodes are operated with direct current or a pulsed current, usually a pulsed direct current. Rectifiers can be used for this. If the number of electrodes exceeds two (i.e. more than one cathode and/or more than one anode), the additional electrodes are preferably operated through an additional rectifier. Within the framework of the present invention it is also possible for each electrode to be supplied by another rectifier in at least one operating region (cathodic, anodic), while in another operating region several rectifiers are connected to one electrode.

Insoluble or soluble anodes can be used as anodes in the method according to the invention. The insoluble anodes typically consist of an inert material (or oxides thereof), such as, for example, lead, graphite, titanium, platinum and/or iridium (and/or oxides thereof). Preferred insoluble anodes are made of titanium coated with platinum or iridium and/or ruthenium (and/or oxides thereof). A titanium anode coated with iridium or iridium oxide is particularly preferred. On the other hand, the soluble anodes consist of the metal to be coated or the metal alloys to be coated. Examples of suitable soluble anodes are anodes made of copper or tin.

Suitable cathodes can consist of the same material as the material of the anodes. A copper cathode can be used, for example, as cathode. In a preferred embodiment, copper electrodes are used both as anode and as cathode, especially if copper is to be deposited on the surface of the flat metal workpiece.

As discussed in the description of the electrically conductive liquid according to the invention, the treatment liquid can comprise an additive, such as, for example, 1,8-dihydroxy-3,6-dithiaoctane (DTO). The intervention of DTO into the anodic erosion and cathodic deposition processes leads, for example, in the case of zinc, copper, nickel, iron, tin and bismuth, to the deposition of very firmly adhering submicro- and microcrystalline aggregates on the surfaces of the substrate to be modified. The possible addition of, for example, DTO—without this being decomposed in the electrolytic process—is therefore a decisive technical advantage of the metal and mixed metal-diphosphonate treatment liquids.

A substantial advantage of using the treatment liquid comprising diphosphonate metal complexes in the method according to the invention is that during continuous operation the diphosphonate suffers no creeping hydrolysis like, for example, the structurally related and similarly acting pyrophosphates. Furthermore, the diphosphonate itself is an excellent buffer, it itself causes an excellent scatter of the deposited layer and needs no auxiliary buffer, such as carbonate or the toxic borate. In a preferred embodiment of the method according to the invention the use of additional buffers, such as e.g. carbonates, borates, acetates or mixtures thereof, in the treatment liquid is therefore omitted. The diphosphonate treatment liquids moreover have excellent scatter properties in the structure of the deposition, with the result that in the method according to the invention the addition of scatter improving agents, such as gelatine, or levelling agent can be omitted.

It has furthermore been found, surprisingly, that the diphosphonate ion itself is capable of initiating the anodic erosion reaction, and that a treatment liquid comprising a diphosphonate complex thus requires no hard anions, such as sulphate or chloride, in order to break the passivation of the anode surface. This is of advantage in particular since, as described above, at the anode the hard anions lead inter alia to the side reaction of creeping oxidation and destruction of the diphosphonate ion. In a specific embodiment of the method according to the invention the treatment liquids are therefore substantially free from sulphate and halide ions. The designation “substantially free” in the context of this invention means a residual concentration of these ions of less than 45 ppm (weight) for halides and of less than 120 ppm (weight) for sulphate.

Without these hard added ions which initiate the secondary anodic oxidation process, electrically conductive treatment liquids based on diphosphonate also form optimum prerequisites for use in the presence of oxidation-sensitive control additives. The treatment liquid used in the method according to the invention can thus comprise additives which influence the viscosity, thermal conductivity, electrical conductivity and/or the deposition of the metal aggregates, without these being decomposed during the method.

Depending on the components used in the treatment liquids, various particularly advantageous actions with respect to the method itself or the modified surface produced by means of the method can be achieved by the method according to the invention for the electrolytic surface modification of flat metal workpieces.

For example, the layers deposited from the lanthanoid-zirconium treatment liquids with zinc, copper, nickel, cobalt, iron, tin and/or bismuth also show an extreme resistance to corrosion on copper. This is particularly striking and interesting in the case of iron and tin. The drying speed of the iron layers on copper plays practically no role in the case of deposition from the diphosphonates. In contrast to this, iron deposited from acid treatment liquids already corrodes during the rinsing operation after the coating.

In the case of tin a certain selectivity of the mixtures emerges: The mixed diphosphonate treatment liquids based on tin-gadolinium-diphosphonate (75 mol % Sn, 25 mol % Gd) deliver, with the addition of 0.1 to 0.5 mol % of DTO, very stable tin layers consisting of strong columns on tin or on copper. The surface is stable to storage and shows good adhesion properties. Similar advantages are to be seen in the case of the tin layers which are deposited from the mixed diphosphonate treatment liquids with tin and zirconium (Sn at least 25 mol %, Zr (1:4) at least 11 mol %). Although zirconium is detected only in the ppm range in the tin layer on steel or on copper, these layers do not tend or tend significantly less towards yellowing or greying under exposure to heat close to the melting point of tin. This also applies to already melted-down tin layers from this deposition.

By the combination of the diphosphonates of e.g. Ni(II) (19 mol %), Gd(III) (76 mol %), Tb(III) (5 mol %) and the addition of DTO (0.1 to 0.5 mol %), nickel is accessible to surface structuring. The small, grey-black looking nickel aggregates on the nickel surface are firmly adhering and deliver a significantly increased adhesion to the plastics and adhesive films pressed on.

The use of the diphosphonate mixed treatment liquids of the metal ions to be deposited, such as Zn, Cu, Ni, Co, Fe, Sn, Bi and the diphosphonate solutions of Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb and Lu allows controllably adjustable deposition of layers, doped with lanthanoid metals, of the host metals mentioned which can also be deposited from aqueous solution alone. The concentrations of the Ln dopants can achieve from a fraction of a percent (Gd—Sn) up to 20 mol % (Sm—Co), depending on the system.

In one embodiment of the method according to the invention layers of Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co or mixtures thereof, as host metals, and Ti, Zr, Nb, Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or mixtures thereof, as doping metals, are deposited on the flat metal workpieces. The doping metals are preferably deposited in a concentration in the range of from 1 ppm to 20,000 ppm, based on the host metals. The relative amount of doping metal can be adjusted by varying the average current density of the deposition and varying the concentration ratio (preferably in the range of from 1:5 to 150:1) between the doping metal and host metal in the treatment liquid.

In a further embodiment of the method according to the invention potentially strongly ferromagnetic, closed layers with an application in the range of from 10 nm to 1 μm of the metals Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co or mixtures thereof doped with Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or mixtures thereof are deposited which have a greater layer thickness of the changeover between the in-plane and the out-of-plane orientation of the domains than in the case of ferromagnetic, pure metal layers deposited by vacuum.

The method according to the invention is also suitable in particular for deposition of corrosion-stable iron and/or tin surfaces and of recrystallization-inhibited tin surfaces.

Some devices for carrying out the method according to the invention are illustrated by way of example in the following.

The devices comprise at least one container for accommodating a treatment liquid, at least one cathode arranged in the container and at least one anode arranged in the container, wherein the at least one cathode and the at least one anode are connected to a current source and wherein the flat metal workpiece is not connected to a current source.

Preferably, at least one cathode and/or at least one anode of the device is designed as flow electrode comprising an electrode housing with a metal mesh through which the treatment liquid (also called electrolyte in the following) can enter into the housing, wherein the electrode housing is at least partially filled with metal balls which are in contact with each other and with the metal mesh. The electrode housing further comprises an electrolyte feed for introducing an electrolyte and a flow opening from which the electrolyte which has flowed through from the electrolyte feed between the metal balls through to the flow opening exits. The flow opening is arranged such that adequate flow takes place through the operating zone, i.e. the space between electrode and flat metal workpiece. For this, the flow opening is usually arranged so that the exiting electrolyte flows past the metal mesh. The flowing past preferably takes place substantially parallel to the metal mesh. During operation, a substantially laminar flow results in this manner in the space between the electrode and the flat metal workpiece, which is preferably a metal strip running through or a metal foil running through.

In addition, the electrode housing usually comprises a cover, in order to prevent the metal balls from falling out and to ensure a defined flow of electrolyte through the flow electrode. The cover can be connected detachably, for example with knurled screws, to the electrode housing and furthermore comprise contacts for connecting to a current source. During operation, the flow electrode is connected anodically or cathodically to a current source, wherein the metal mesh is usually contacted anodically or cathodically.

The electrolyte which has flowed through the metal balls is preferably collected in an electrolyte channel and then supplied to the flow opening. The electrolyte channel and the flow opening are preferably located in the base of the electrode housing. The flow opening is preferably designed as a flow lip which preferably extends over the entire length of the metal mesh in the base of the electrode housing. If a filter nonwoven arranged in front of the metal mesh is used as an anode bag, the flow opening is arranged such that the electrolyte exits in front of the filter nonwoven and flows along the latter substantially laminar.

The electrode housing can, for example, consist of a plastic, such as polypropylene. The metal balls can consist of the metals named above for the anode and cathode. Preferably, at least one anode is designed in the form of the flow electrode described above. In the case of the anode the metal balls preferably consist of the metal or the metals which is or are to be deposited on the flat metal workpiece. The metal balls are preferably copper balls. The metal mesh is preferably an expanded metal mesh (expanded metal screen area), in particular a titanium expanded metal.

FIG. 1 shows schematically an embodiment of a dissolving/deposition cell 30 for carrying out the method according to the invention for surface treatment of a flat metal workpiece 32, in this case a metal foil. The dissolving/deposition cell 30 has a trough-like container 31, open at the top, in which treatment liquid 36 is located. The dissolving/deposition cell 30 further has a first, second and third guide roller 34 a, 34 b and 34 c and a first working electrode, which consists of two cathodes 40 a and 40 b arranged parallel, and a second working electrode, which consists of two anodes 44 a and 44 b arranged parallel. The cathodes 40 a and 40 b and the anodes 44 a and 44 b are connected to a current source 45. The first and third guide roller 34 a, 34 c are arranged above the container 31 outside the treatment liquid 36 and above the first and second working electrodes, while the second guide roller is located at the base of the container 31 within the treatment liquid and below the working electrodes. Furthermore, the dissolving/deposition cell 30 has a separating element 48 for reducing blind currents.

The flat metal workpiece 32 runs into the treatment liquid 36 via the first guide roller 34 a and through between the two cathodes 40 a, 40 b, with the result that these are located in each case on one of the two sides of the flat metal workpiece 32 passing through. Neither the flat metal workpiece 32 nor the first guide roller 34 a is connected to a current source. The region 38 a of the flat metal workpiece 32 located between the two cathodes 40 a, 40 b is positively (anodically) polarized by the two cathodes 40 a, 40 b. The two cathodes 40 a, 40 b define a dissolving region 42. In the enlarged and schematically represented section of the dissolving region 42, impurities and possibly occurring foreign metals and/or particular (e.g. uneven) metal structures present on the surface of the flat metal workpiece 32 are largely eliminated. As a result, an impurity-free, homogeneous and defined surface of the flat metal workpiece 32 is obtained which is suitable for achieving defined metal structures in the subsequent deposition step.

After passing through the cathodes 40 a, 40 b, i.e. the dissolving region 42, the flat metal workpiece 32 is guided via the second guide roller 34 b, which likewise is not connected to a current source, between the two anodes 44 a, 44 b, which are located in each case on one of the two sides of the flat metal workpiece 32 and form the second working electrode. A region 38 b of the flat metal workpiece 32 is negatively (cathodically) polarized by the two anodes 44 a, 44 b. The two anodes define a deposition region 46. In the enlarged and schematically represented section of the deposition region 46, the positively charged metal ions of the treatment liquid 36 migrate to the negatively polarized surface of the flat metal workpiece 32 and are deposited in a defined manner on the surface of the flat metal workpiece 32. After passing through the deposition region 46, the flat metal workpiece 32 runs out of the treatment liquid 36 and over the third guide roller 34 c, which is not connected to a current source.

The flat metal workpiece 32 treated electrolytically in this manner with a treatment liquid according to the invention has on the surface thereof defined metal aggregates in the submicrometre range and shows surprisingly good adhesion and adhesive properties.

Alternatively to the embodiment described in FIG. 1 according to the closed neutral conductor principle (NCP), different treatment liquids can be used in the dissolving region 42 and in the deposition region 46, these being separated by a dense, non-conductive separating liquid which is inert in the process and also has contact with the flat metal workpiece. In this manner the closed NCP of FIG. 1 becomes an open NCP having separated erosion and deposition zones, and the substrate can be eroded in the dissolving region and coated with elements foreign to the substrate in the deposition region, with continuous wetting and cooling.

FIG. 2 describes by way of example such an apparatus for carrying out a method according to the open neutral conductor principle by the example of tin-plating of copper foil. A trough-like container (CW), open at the top, of polypropylene having a container wall thickness of 20 mm which is divided by a 15 mm thick polypropylene dividing wall (DW) into a dissolving and a deposition zone, wherein the dividing wall does not extend completely to the base of the container, is used as the dissolving/deposition cell. At the base of the container there is a dense, non-conductive, separating liquid which is inert in the process, extends to above the lower edge of the dividing wall and forms a separating agent zone (SA) in the container. Above this separating agent zone, in the dissolving zone there is a copper-diphosphonate-DTO electrolyte (CuE), the level of liquid of which reaches to an overflow opening (OF-Cu) in the dissolving zone of the container. In the deposition zone, over the separating agent zone lies a tin-gadolinium-diphosphonate-DTO electrolyte (SnGdE), the level of liquid of which reaches to an overflow opening (OF-Sn) in the deposition zone of the container. An auxiliary cathode (AC), which comprises copper balls (Cu) enclosed by a titanium expanded metal window (TiW), is immersed in the copper-diphosphonate-DTO electrolyte. An auxiliary anode (AA), which comprises tin granules (Sn) enclosed by a titanium expanded metal window (TiW), is immersed in the tin-gadolinium-diphosphonate-DTO electrolyte. The inflow of the copper-diphosphonate-DTO electrolyte (IF-Cu) takes place in the dissolving zone over the auxiliary cathode, that of the tin-gadolinium-diphosphonate-DTO electrolyte (IF-Sn) in the deposition zone over the auxiliary anode, as shown in FIG. 2. The stripping nozzles SN-Cu and SN-SA serve for complete detachment of the previous medium from the foil surface, also called turbulent stripping. The cleaning circulation (CC-SA) is the extractive washing/treatment of the separating agent to remove entrained electrolyte residues. The dissolving/deposition zones furthermore each have two guide rollers (GR), wherein in each case one is arranged above the electrolyte and in each case one in the separating agent zone. The flat copper workpiece runs in the strip or foil running direction (SRD) over the first guide roller into the treatment liquid comprising the copper-diphosphonate-DTO electrolyte and past the auxiliary cathode in the dissolving zone, as a result of which the flat metal workpiece positively (anodically) polarizes and an erosion of impurities and uneven metal structures present on the surface of the flat copper workpiece takes place. As a result an impurity-free, homogeneous and defined surface is obtained on the copper workpiece, which is suitable for achieving defined metal structures in the subsequent deposition step. The copper workpiece then enters into the separating agent zone and is conveyed from there by means of the guide rollers located therein into the deposition zone under constant liquid contact. On passing the auxiliary anode, the copper workpiece is negatively (cathodically) polarized here and positively charged tin ions are deposited from the tin-gadolinium-diphosphonate-DTO treatment liquid on the negatively charged copper surface of the copper workpiece in a defined manner. Gadolinium can likewise be deposited in the ppm range together with the tin. After passing through the deposition zone, the tin-plated copper workpiece runs out of the treatment liquid SnGdE.

It has been found that the metal or the metals which are deposited according to the method according to the invention do not cover the surface of the flat metal workpiece continuously, but rather in the form of uniformly distributed, discrete metal aggregates. The present invention therefore also relates to the flat metal workpieces produced with this method, the surfaces of which are provided with metal aggregates. These metal aggregates are metal growths on the surface of the flat metal workpiece, produced by the electrolytic deposition of one or more metals. The metal aggregates as a rule are present in uniform distribution on the surface and can have a varying appearance. Compact aggregates on a crystalline basis with a varying habit are typical. The size of the metal aggregates as a rule lies in the submicrometre range (<1 μm). Typically, 90% or more (more preferably 95% or more, in particular 99% or more) of the metal aggregates have a size in the range of from 0.05 to 1 μm, preferably in the range of from 0.3 to 0.7 μm and in particular in the range between 0.35 and 0.65 μm. The size relates to the average diameter of the metal aggregates deposited, determined with the aid of electron microscope photographs.

FIG. 3 shows an SEM photograph of a copper foil treated in the closed NCP with the electrolytically obtained Cu-DTO-diphosphonate electrolyte. The surface, here also described as vsbp (very small black pyramids) looks brown to black, depending on the aggregate density. It is presumed that the black colour is a physical extinguishing process of the light due to interference on the surface. The tiny aggregates shown have grown with their lattice plane base on to the previously eroded foil and show flat crystal faces. They consist (in the context of measurement accuracy) exclusively of copper. The layer thickness is less than 0.5 μm. The extension in the plane of the foil is in the range of from 30 nm to 300 nm.

The roughness of the metal surface increases to a small extent through the deposition of the metal aggregates. After the deposition of the metal aggregates, in particular of copper aggregates, on to a flat metal workpiece, in particular on to a copper foil or strip, the average roughness values Ra and Rz, determined in accordance with DIN EN ISO 4288:1998, are preferably in the range of from 0.22 to 0.32 μm for Ra and in particular in the range of from 0.24 to 0.28 μm for Ra, and preferably in the range of from 1.4 to 2.1 μm for Rz and in particular in the range of from 1.6 to 1.9 μm for Rz. In contrast, before the deposition, a copper foil has, for example, roughness values of about 0.20 μm for Ra and 1.3 μm for Rz.

These specific metal aggregates are responsible for the surface obtained having outstanding adhesive properties (adhesion properties) and being excellently suitable as substrate for the formation of strong adhesive bonds with a plurality of materials. The increase in the adhesive strength is primarily explained by the fact that the metal aggregates protrude from the surface of the flat metal workpiece and serve virtually as “anchor points” for the adhesion partner. In particular, the metal aggregates on the surface of the flat metal workpiece lead to a strong adhesive bond on pressing or rolling (roll cladding) with the same or another material, on lacquering with or without subsequent curing/crosslinking or on gluing. A plurality of materials come into consideration as adhesion partner for the metal workpiece according to the invention, for example thermoplastics, such as PA 66, PI and PET, synthetic resins (epoxides), adhesives, lacquers and pastes, such as graphite pastes.

The present invention therefore also relates to the use of the metal workpieces produced according to the method according to the invention as substrate for the formation of strong adhesive bonds with other materials, such as, for example, thermoplastics, synthetic resins, adhesives, lacquers and pastes.

With the aid of the method according to the invention, using corresponding treatment liquids based on metal-diphosphonate complexes, layers of one or more different metals structured over the area can furthermore also be applied, including as dopants in the layer also those metals which normally cannot be deposited electrolytically from aqueous solution. Flat layers which have a high potential for use in the sensor technology of magnetic fields and the accommodation of/conversion into catalytically active centres in the layer can also be applied. The present invention therefore also relates to the use of the metal workpieces produced according to the method according to the invention as base materials for the production of GMR sensors or Hall effect sensors (detection of magnetic fields), and as base materials, the surface of which can be converted by oxidation into catalytically active mixed oxides and very thin oxide ceramics, analogously to LNO layers.

Further examples of the large number of uses for which the flat metal workpieces produced according to the method according to the invention can be used are, inter alia, laminates of copper with PET for the shielding of cables and plug and appliance housings from electromagnetic interferences, in particular in signal transmission. Furthermore, the use as electrical conductor in the production of MID (moulded interconnect devices) circuits is to be mentioned. These are circuits which are based on hot stamping of metallic foils on thermoplastic substrates. A further application is as substrate for electrode material in battery technology. In particular, the flat metal workpieces according to the invention can also be used in the production of stable connections required in circuit-board technology for the production of copper laminates. Specifically in the production of circuit boards, the adhesive strength of the metallic conductor on the substrate (e.g. FR-4) is of central importance. This is due on the one hand to the process steps necessary in the production (etching, drilling, pressing) and on the other hand to the load on the circuit board in the end product itself.

EXAMPLES Preparation of Diphosphonate Electrolytes Preparation from Metal Oxides and Diphosphonic Acid Synthesis Example 1 Electrolyte A—Copper-diphosphonate-DTO Electrolyte

327.5 g of de-ionized water and 466.7 g of a 60% strength aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid (Cublen K60, obtainable from Zschimmer & Schwarz, 09217 Burgstadt, Germany) are mixed in a 2,000 ml glass beaker by stirring. 54.5 g of finely powdered blue-black copper(II) oxide is introduced at 60° C. in the course of 30 minutes, while stirring. The oxide initially dissolves, and then forms a deep blue slurry. After the end of the addition the glass beaker is placed in a water bath of room temperature. After 10 minutes the slow, continuous addition of 461.3 g of potassium hydroxide solution 45% (D=1.46 g/cm³) is cautiously started, while stirring/kneading vigorously. The temperature is controlled during the addition. The reaction temperature is always kept at ≦90° C. After 20 minutes the addition of the potassium hydroxide solution has ended. The solution obtained is kept at 90° C. for a further 2 h, wherein the evaporation loss is constantly compensated for by addition of further de-ionized water. Thereafter cooling to 25° C. is carried out and the pH is adjusted to 8.5 to 10 with potassium hydroxide. The deep blue solution obtained is filtered at room temperature over a filter (<50 μm) charged with active charcoal, and after the filtration the filtrate is topped up to 1,000 ml with de-ionized water.

The copper-diphosphonate electrolyte A obtained is a colourless liquid having a pH of 9.2±0.5 and a density of 1.31 g/cm³ at 25° C. The molar ratio of Cu:P:K is 1:4.0±0.2:5.4±0.4 (determined by optical emission spectrometry with inductively coupled plasma (ICP-OES), 6% strength nitric acid).

The above solution was then heated to 60° C. and a total of 0.1 wt. %, based on the total weight of the electrolyte, (1.31 g) of 1,8-dihydroxy-3,6-dithiaoctane (DTO) was added in stages, while stirring thoroughly, in order to obtain the copper-diphosphonate-DTA electrolyte. The DTO dissolves completely within less than 2 minutes.

Synthesis Example 2 Electrolyte B—Bismuth-diphosphonate Electrolyte

344.6 g of de-ionized water and 438.1 g of a 60% strength aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid (Cublen K60, obtainable from Zschimmer & Schwarz, 09217 Burgstadt, Germany) are mixed in a 2,000 ml glass beaker by stirring. 95.6 g of finely powdered, yellow bismuth(III) oxide is introduced in the course of 30 minutes, while stirring. The oxide initially dissolves, and then forms a white slurry and a yellow sediment. After the end of the addition the glass beaker is placed in a water bath of room temperature. A titanium sonotrode is positioned in the centre of the glass beaker and switched on. After 10 minutes the slow, continuous addition of 476.7 g of potassium hydroxide solution 45% (D=1.46 g/cm³) is cautiously started. During the addition the ultrasound treatment and addition are interrupted for the purpose of controlling the temperature. The reaction temperature is always kept at ≦85° C. After 30 minutes the addition of the potassium hydroxide solution and the ultrasound treatment are ended. The solution obtained is kept at 90° C. for a further 6 h, wherein the evaporation loss is constantly compensated for. Thereafter cooling to 25° C. is carried out and the pH is adjusted to 8.5 to 9.5 with potassium hydroxide.

The colourless solution obtained may still have a slight cloudiness, which is lost by storage for 24 h. If the cloudiness remains, filtering is carried out over a filter (<50 μm) charged with active charcoal, and after the filtration the filtrate is topped up to 1,000 ml with de-ionized water.

The bismuth-diphosphonate electrolyte B obtained is a colourless liquid having a pH of 8.8±0.3 and a density of 1.355 g/cm³ at 25° C. The molar ratio of Bi:K:P is 1:7.6±0.4:6.4±0.3 (determined by ICP-OES, 6% strength nitric acid).

Synthesis Example 3 Electrolyte C—Cobalt-diphosphonate Electrolyte

360 g of de-ionized water and 466 g of a 60% strength aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid (Cublen K60, obtainable from Zschimmer & Schwarz, 09217 Burgstadt, Germany) are mixed in a 2,000 ml glass beaker by stirring. 81.3 g of finely powdered, pink cobalt(II) carbonate is introduced in the course of 60 minutes, while stirring. The carbonate initially dissolves rapidly, and then forms a pale pink slurry. After the slurry formation starts in particular, the addition must take place cautiously, in order to avoid foaming over of the reaction vessel (escaping reaction gas carbon dioxide). Immediately after the end of the addition and the evolution of gas the glass beaker is placed in a water bath of room temperature. Without a pause and while stirring/kneading vigorously, the slow, continuous addition of 412.4 g of potassium hydroxide solution 45% (D=1.46 g/cm³) is cautiously started. During the addition the temperature is controlled constantly, wherein the reaction temperature is always kept at 85° C. After 15 minutes the addition of the potassium hydroxide solution has ended. The solution obtained is then kept at 90° C. for 1 h, wherein the evaporation loss is constantly compensated for. Thereafter cooling to 25° C. is carried out and the pH is adjusted to 9.0 to 10 with potassium hydroxide. The intensely pink solution is filtered over a filter (<50 μm) charged with active charcoal, and after the filtration the filtrate is topped up to 1,000 ml with de-ionized water. The cobalt-diphosphonate electrolyte C obtained is a pink liquid having a pH of 9.5±0.5 and a density of 1.32 g/cm³ at 25° C. The molar ratio of Co:P:K is 1:4.0±0.2:4.9±0.3 (determined by ICP-OES, 6% strength nitric acid).

Synthesis Example 4 Electrolyte D—Zinc-diphosphonate Electrolyte

325.6 g of de-ionized water and 464 g of a 60% strength aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid (Cublen K60, obtainable from Zschimmer & Schwarz, 09217 Burgstadt, Germany) are mixed in a 2,000 ml glass beaker by stirring. 91.8 g of fine-flaked, black tin(II) oxide is introduced in the course of 60 minutes, while stirring. The oxide initially dissolves slowly, and then forms a white slurry and a grey sediment. After the end of the addition the mixture is subsequently stirred for a further 4 h. Thereafter the glass beaker is placed in a water bath of room temperature. After 10 minutes the slow, continuous addition of 458.5 g of potassium hydroxide solution 45% (D=1.46 g/cm³) is cautiously started, while stirring/kneading. The reaction temperature is controlled during the addition. The reaction temperature is always kept at 80° C. After 30 minutes the addition of the potassium hydroxide solution has ended. The solution obtained is kept at 80° C. for a further 6 h, wherein the evaporation loss is constantly compensated for. Thereafter cooling to 25° C. and storage for a further 48 h are carried out. The pH is adjusted to 9.0 to 10 with potassium hydroxide.

The colourless solution obtained still has a colourless cloudiness and an oily covering film and is filtered over a filter (<50 μm) charged with active charcoal. After the filtration the filtrate is topped up to 1,000 ml with de-ionized water.

The tin-diphosphonate electrolyte D obtained is a colourless liquid having a pH of 9.4±0.3 and a density of 1.34 g/cm³ at 25° C. The molar ratio of Sn:P:K is 1:4.9±0.3:8.5±0.5 with a variable Sn(II):Sn(IV) ratio (determined by ICP-OES, 6% strength nitric acid).

Synthesis Example 5 Electrolyte E—Erbium-diphosphonate Electrolyte

377 g of de-ionized water and 504.6 g of a 60% strength aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid (Cublen K60, obtainable from Zschimmer & Schwarz, 09217 Burgstadt, Germany) are mixed in a 2,000 ml glass beaker by stirring. 141.6 g of finely powdered, red erbium(III) oxide is introduced in the course of 20 minutes, while stirring. The oxide initially dissolves, and then forms a red slurry and a red sediment. After the end of the addition the glass beaker is placed in a water bath of room temperature. A titanium sonotrode is positioned in the centre of the glass beaker and switched on. After 10 minutes the slow, continuous addition of 446.7 g of potassium hydroxide solution 45% (D=1.46 g/cm³) is cautiously started. During the addition the ultrasound treatment and addition are interrupted for controlling the temperature. The reaction temperature is always kept at ≦90° C. After 30 minutes the addition of the potassium hydroxide solution and the ultrasound treatment are ended. The solution obtained is kept at 90° C. for a further 2 h, wherein the evaporation loss is constantly compensated for. Thereafter cooling to 25° C. is carried out and the pH is adjusted to 8.5 to 9.5 with potassium hydroxide.

The red solution obtained should not be cloudy. If a cloudiness remains, the filtering is carried out over a filter (<50 μm) charged with active charcoal, and after the filtration the volume is topped up to 1,000 ml with de-ionized water.

The erbium-diphosphonate electrolyte E obtained is a raspberry red liquid having a pH of 9.0±0.5 and a density of 1.43 g/cm³ at 25° C. The molar ratio of Er:P:K is 1:4.0±0.2:4.8±0.3 (determined by ICP-OES, 6% strength nitric acid).

Synthesis Example 6 Electrolyte F—Terbium-diphosphonate Electrolyte

By reworking synthesis example 5, but replacing the erbium(III) oxide by 138.4 g of terbium(III/IV) oxide, terbium-diphosphonate electrolyte F was obtained as a pale green liquid having a pH of 9.0±0.5, a density of 1.43 g/cm³ and a molar ratio of Tb:P:K of 1:4.0±0.2:4.8±0.3.

Synthesis Example 7 Electrolyte G—Gadolinium-diphosphonate Electrolyte

318 g of de-ionized water and 465.8 g of a 60% strength aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid (Cublen K60, obtainable from Zschimmer & Schwarz, 09217 Burgstadt, Germany) are mixed in a 2,000 ml glass beaker by stirring. 123.8 g of finely powdered, colourless gadolinium(III) oxide is introduced in the course of 30 minutes, while stirring. The oxide initially dissolves exothermically, and then forms a white slurry and a colourless sediment. After the end of the addition the glass beaker is placed in a water bath of room temperature. After 10 minutes the slow, continuous addition of 412.4 g of potassium hydroxide solution 45% (D=1.46 g/cm³) is cautiously started, while stirring/kneading vigorously. The temperature of the reaction mixture is constantly controlled during the addition. The reaction temperature is always kept at ≦90° C. After 20 minutes the addition of the potassium hydroxide solution has ended. The solution obtained is kept at 90° C. for a further 2 h, wherein the evaporation loss is constantly compensated for. Thereafter cooling to 25° C. is carried out and the pH is adjusted to 8.5 to 9.5 with potassium hydroxide.

The colourless solution obtained still has a slight cloudiness, which can be lost by storage for 24 h. If the cloudiness remains, filtering is carried out over a filter (<50 μm) charged with active charcoal. After the filtration the filtrate is topped up to 1,000 ml with de-ionized water.

The gadolinium-diphosphonate electrolyte G obtained is a colourless liquid having a pH of 9.0±0.5 and a density of 1.32 g/cm³ at 25° C. The molar ratio of Gd:P:K is 1:4.0±0.2:4.8±0.3 (determined by ICP-OES, 6% strength nitric acid).

Synthesis Example 8 Electrolyte H—Neodymium-diphosphonate Electrolyte

275.6 g of de-ionized water and 472.9 g of a 60% strength aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid (Cublen K60, obtainable from Zschimmer & Schwarz, 09217 Burgstadt, Germany) are mixed in a 2,000 ml glass beaker by stirring. 77.2 g of finely powdered, blue neodymium(III) oxide is introduced in the course of 30 minutes, while stirring. The oxide initially dissolves highly exothermically, and then forms a violet slurry. After the end of the addition the glass beaker is placed in a water bath of room temperature. After 10 minutes the slow, continuous addition of 514.3 g of potassium hydroxide solution 45% (D=1.46 g/cm³) is cautiously started, while stirring/kneading thoroughly. The temperature of the reaction mixture is constantly monitored during the addition. The reaction temperature is always kept at ≦90° C. After 20 minutes the addition of the potassium hydroxide solution has ended. The solution obtained is kept at 90° C. for a further 1 h, wherein the evaporation loss is constantly compensated for. Thereafter cooling to 25° C. is carried out and the pH is adjusted to 9.0 to 9.8 with potassium hydroxide. At the end it is topped up to 1,000 ml with de-ionized water.

The neodymium-diphosphonate electrolyte H obtained is a red-violet liquid having a pH of 9.4±0.4 and a density of 1.34 g/cm³ at 25° C. The molar ratio of Nd:P:K is 1:6.0±0.4:9.0±0.5 (determined by ICP-OES, 6% strength nitric acid).

Synthesis Example 9 Electrolyte I—Nickel-gadolinium-diphosphonate Electrolyte

324.8 g of de-ionized water and 465.8 g of a 60% strength aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid (Cublen K60, obtainable from Zschimmer & Schwarz, 09217 Burgstadt, Germany) are mixed in a 2,000 ml glass beaker by stirring. First of all 12.7 g of finely powdered, apple-green nickel(II) hydroxide and directly following this 99.0 g of finely powdered gadolinium(III) oxide are introduced in the course of 30 minutes, while stirring. The oxides initially dissolve, and then form a pale yellow slurry and an almost colourless sediment, which should contain no green contents. After the end of the addition of the oxides the glass beaker is placed in a water bath of room temperature. Without a pause, the slow, continuous addition of 417.6 g of potassium hydroxide solution 45% (D=1.46 g/cm³) is cautiously started, while stirring/kneading vigorously. The reaction temperature is controlled during the addition and is always kept at ≦90° C. After 20 minutes the addition of the potassium hydroxide solution has ended. The solution obtained is kept at 90° C. for a further 2 h, wherein the evaporation loss is constantly compensated for. Thereafter cooling to 25° C. is carried out and the pH is adjusted to 8.5 to 9.5 with potassium hydroxide. The green-yellow solution obtained may still have a slight cloudiness, which is lost by storage for 24 h. If the cloudiness remains, filtering is carried out over a filter (<50 μm) charged with active charcoal, and after the filtration the filtrate is topped up to 1,000 ml with de-ionized water.

The nickel-gadolinium-diphosphonate electrolyte I obtained is a green-yellow liquid having a pH of 9.0±0.5 and a density of 1.32 g/cm³ at 25° C. The molar ratio of [Gd+Ni]:P:K is 1:4.1±0.3:4.4±0.3 with an Ni:Gd ratio of 1:3.9 (determined by ICP-OES, 6% strength nitric acid).

Synthesis Example 10 Electrolyte J—Nickel-gadolinium-terbium-diphosphonate Electrolyte with Addition of 0.5 Mol % of DTO

1,000 ml of this electrolyte is prepared by blending 950 ml (1,254 g) of nickel-gadolinium-diphosphonate electrolyte I from synthesis example 9 with 50 ml (70.5 g) of terbium(III)-diphosphonate electrolyte F from synthesis example 6.

The nickel-gadolinium-terbium-diphosphonate solution obtained is then heated to 60° C. and a total of 0.5 wt. %, based on the total weight of the electrolyte, (5.5 g) of 1,8-dihydroxy-3,6-dithiaoctane (DTO) is added in stages, while stirring thoroughly, in order to obtain electrolyte J as a green-yellow liquid having a pH of 9.0±0.5, a density of 1.32 g/cm³ at 25° C., a molar ratio of [Gd+Tb+Ni]:P:K of 1:4.0±0.3:4.5±0.3 and an Ni:Gd:Tb ratio of 1:3.9:0.2 (ICP-OES, 6% strength nitric acid).

Preparation by Metallization Synthesis Examples 11-14 Electrolytes K, L, M and N—Copper-diphosphonate-DTO Electrolytes

336.4 g of de-ionized water and 451.7 g of a 60% strength aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid (Cublen K60, obtainable from Zschimmer & Schwarz, 09217 Burgstadt, Germany) are mixed in a 2,000 ml glass beaker by stirring. The glass beaker is placed in a water bath of room temperature. Thereafter the slow, continuous addition of 491.9 g of potassium hydroxide solution 45% (D=1.46 g/cm³) is cautiously started, while stirring thoroughly. The temperature is controlled during the addition. The reaction temperature is always kept at 80° C. After 20 minutes the addition of the potassium hydroxide solution has ended. Thereafter cooling to 25° C. is carried out and the pH is adjusted to 6.5 to 8.5 with potassium hydroxide or diphosphonate.

The colourless solution obtained is clear and is topped up to 1,000 ml with de-ionized water. The colourless liquid has a pH of 8.8±0.3, a density of 1.27±0.02 g/cm³ at 25° C. and a molar ratio of K:P of 1.5:1 (ICP-OES, 6% strength nitric acid).

Two 8 mm copper anodes are introduced into a separate 1,000 ml glass beaker, in the centre a copper cathode of 0.5 mm copper sheet. The electrodes are blinded from each other with two 0.3 mm HDPE sheets. The ratio of the immersed anode surface to the cathode surface is 10:1. The cathode is bound with a collecting bag of PP fibre in order to keep copper which is unintentionally deposited and partially split off away from the solution. 860 ml (=1,100 g) of the colourless solution obtained above is then poured in. The apparatus is provided with a magnetic stirring rod and positioned on a magnetic stirrer in a water bath. The apparatus is stirred at 600 rpm, a rectifier is connected and the maximum possible current strength (23 A) is applied. For the current supply a power unit of the Statron model 3254.1 type with pre-selectable current strength and display of the corresponding voltage is used. A pole-inverter switch is located between the power unit and the electrolytic cell, whereby the polarity of the foil and of the electrodes can be reversed (switched) in any sequence and at any time during the test.

Due to the electrolysis the temperature rises to 60° C. in the course of 24 minutes, the maximum current density being reached at approx. 48° C. During the metallization the copper content is controlled at intervals of 60 minutes. This increases rapidly at the start and changes further only slowly above 13.5 g/l of copper. After 3×6 h=18 h of metallization the electrolysis is interrupted, the electrodes are removed, and the apparatus is taken out of the water bath and cooled to room temperature. The pH of the solution is then adjusted to about 9.5 with potassium hydroxide (45%) and the apparatus is topped up to 860 ml with de-ionized water. The copper-diphosphonate solution obtained is a deep blue liquid having a pH of 9.5±0.3 and a density of 1.31±0.02 g/cm³ at 25° C. The Cu concentration is 15.3 g/l, the molar ratio of Cu:P:K is about 1:11:14.8 (determined by ICP-OES, 6% strength nitric acid).

The above solution was then heated to 60° C. and a total of 0.05 wt. %, based on the total weight of the electrolyte, (0.56 g) of 1,8-dihydroxy-3,6-dithiaoctane (DTO) was added in stages, while stirring thoroughly, in order to obtain the copper-diphosphonate-DTO electrolyte K. The DTO dissolves completely within 2 minutes. The deep blue colour of the solution is retained unchanged.

Electrolytes L, M and N were prepared in a similar manner but with the addition of in total 1.13 g (0.1 wt. %), 2.26 g (0.2 wt. %) and 5.5 g (0.5 wt. %) of DTO, respectively.

Synthesis Examples 15-18 Electrolytes K1, L1, M1 and N1—Copper-diphosphonate-DTDA Electrolytes

4,7-Dithiadecandioic acid (DTDA) was prepared as described in the U.S. Pat. No. 2,602,816 and recrystallized from boiling water (m.p. 163-164° C.).

Analogously to synthesis examples 11-14, a copper-diphosphonate solution was prepared by metallization. 1.44 g of 4,7-dithiadecanedioic acid (DTDA) (0.11 wt. %, based on the total weight of the electrolyte of 1,000 ml) was then added to the solution at room temperature, while stirring, in order to obtain the copper-diphosphonate-DTDA electrolyte K1. The DTDA dissolves completely within 20 seconds. The deep blue colour of the solution is retained unchanged. The pH of the electrolyte is subsequently adjusted to the range of about 9 by the addition of potassium hydroxide solution (50%).

Electrolytes L1, M1 and N1 were prepared in a similar manner but with the addition of in total 2.75 g (0.21 wt. %), 5.23 g (0.40 wt. %) and 14.4 g (1.10 wt. %) of DTDA, respectively.

Synthesis Example 19 Electrolyte K2—Copper-diphosphonate-DMDTK Electrolyte

Dipotassium 2,9-dimethyl-4,7-dithiadecanedioate (DMDTK) was obtained as follows, analogously to D. M. Haddleton, et al., Polymer Chemistry, 2010, vol. 1, p. 1196 to 2040. Ethanedithiol was reacted with ethyl methacrylate (1:2.2) in acetone under triethylamine catalysis. About 80% of the acetone was distilled off, triethylamine and unreacted ethyl methacrylate were then extracted from the aqueous-acidic from the distillation residue with ice-cold dilute hydrochloric acid, the crude product was then extracted with toluene, and the toluene extract was dried over sodium sulphate/sodium carbonate=3:1 (both anhydrous). The toluene extract was saponified with ethanolic potassium hydroxide in ethanol at 78° C., wherein the potassium salt of 2,9-dimethyl-4,7-dithiadecanedioic acid (dipotassium 2,9-dimethyl-4,7-dithiadecanedioate, DMDTK) precipitated out in the pure form (as a mixture of the diastereomers) on cooling of the reaction solution.

Analogously to synthesis examples 11-14, a copper-diphosphonate solution was prepared by metallization. 4.06 g of dipotassium 2,9-dimethyl-4,7-dithiadecanedioate (DMDTK) (0.31 wt. %, based on the total weight of the electrolyte of 1,000 ml) were then added to the solution at room temperature, while stirring, in order to obtain the copper-diphosphonate-DMDTK electrolyte K2. The DMDTK dissolves completely within 10 seconds. The deep blue colour of the solution is retained unchanged.

Synthesis Examples 20-23 Electrolytes K3, L3, M3 and N3—Copper-diphosphonate-DMDTDA Electrolytes

2,9-Dimethyl-4,7-dithiadecanedioic acid (DMDTDA) was obtained as follows: the toluene and tiny residues of ethyl methacrylate were distilled off in vacuo (50 torr) from the toluene extract obtained in the preparation of dipotassium 2,9-dimethyl-4,7-dithiadecanedioate (DMDTK). The honey-coloured oil obtained was saponified in aqueous 10% strength sodium hydroxide solution and the acid was precipitated by slow pouring of the mixture into stirred dilute hydrochloric acid at room temperature. The crude product was washed with ice-water and thereafter recrystallized from boiling water (m.p. 152-156° C.). 2,9-Dimethyl-4,7-dithiadecanedioic acid (DMDTDA) was obtained as a mixture of the diastereomers.

Analogously to synthesis examples 11-14, a copper-diphosphonate solution was prepared by metallization. The solution was then heated to 60° C. and 1.57 g of 2,9-dimethyl-4,7-dithiadecanedioic acid (DMDTDA) (0.12 wt. %, based on the total weight of the electrolyte of 1,000 ml) was then added, while stirring, in order to obtain the copper-diphosphonate-DMDTDA electrolyte K3. The DMDTDA dissolves completely within 20 seconds. The deep blue colour of the solution is retained unchanged. The pH of the electrolyte is subsequently adjusted to the range of about 9 by the addition of potassium hydroxide solution (50%).

Electrolytes L3, M3 and N3 were prepared in a similar manner but with the addition of 3.15 g (0.24 wt. %), 6.29 g (0.48 wt. %) and 15.7 g (1.20 wt. %) of DMDTDA, respectively.

Surface Modification of Flat Metal Workpieces Example 1 Modification of a Tin-Plated Copper Foil by Deposition of Tin Aggregates on the Foil Surface According to the Closed Neutral Conductor Principle Electrolysis Arrangement

The following static electrolysis arrangement for simulation of the closed neutral conductor principle was used for the surface modification of a tin-plated copper foil:

The static electrolytic cell comprises a 1,000 ml glass beaker filled with an electrolyte (900 ml). The glass beaker stands on a heated stirrer. The heated stirrer is used to heat the electrolyte, wherein the temperature is continuously tested by a thermocouple with a stainless steel sheath and kept constant in a scope of ±2° C. The stirrer speed is kept at 1,000 rpm and the stirring is transmitted to the electrolyte solution by a round magnetic stirring rod (PTFE) of dimensions 40×d6.

Over the glass beaker there is a cover plate of PP, which is laid over the glass beaker and has in each case at a distance of 30 mm on both sides in each case an inert electrode of Ti/IrO₂. These electrodes are flat sheets which are immersed parallel to each other and in each case perpendicularly into the electrolyte solution. The one-side, immersed surface area is between 60 mm×80 mm and 60 mm×100 mm per electrode. In the centre, the plastic plate was provided with an opening of 20 mm×80 mm parallel to the inert electrodes, through which opening the flexible foil holder can be introduced into the cell. This foil holder was therefore formed flexible so that the foil, once inserted, can then pass through the entire process, including the pre-treatment and after-treatment steps (e.g. cleaning/rinse/rinse, etching/pickling/rinse/rinse, electrolysis/rinse/rinse, passivation/rinse/rinse/DI rinse) in the same holder and only needs to be taken out of the holder after the last rinse for drying. The foil holder consists of two PP frames with a window of 80 mm×60 mm, into which the foil is clamped. The clamping screws are manufactured from PA6 plastic. The lower clamping screws serve only to clamp the foil, the upper clamping screws serve in addition to produce a releasable press contact with a TiPt expanded metal mesh. This contact point is immersed in the solution, with the result that the foil is completely immersed in the electrolyte and the contact point is blanked off from the field of the cell by the frame of the foil holder. The expanded metal used for the contacting projects upwards out of the cell and is supplied with current via a crocodile clip. For the current supply, a power unit of the Statron type with pre-selectable current strength and display of the corresponding voltage is used. A pole-inverter switch is located between the power unit and the electrolytic cell, whereby the polarity of the foil and of the electrodes can be reversed (switched) in any sequence and at any time during the test.

Surface Modification

A tin-plated copper foil having a pure tin application of about 2 μm, a copper layer thickness of 35 μm, a length of 8.5 cm (effective) and a width of 5.0 cm was first subjected to a pre-treatment which comprised the following steps in the stated sequence:

-   -   Precleaning: Purax 6029PUS, 40 g/l, 60° C., currentless, 10 s.     -   Rinse: Water     -   Fine cleaning: Velocit 1127M, 25 g/l, 60° C., currentless, 10 s.     -   Rinse: Water     -   Etching/pickling: Sulphuric acid (7% strength in water), 25°         C.-35° C.     -   Rinse: Water

The copper foil pre-treated in this way was then surface-modified in the static electrolysis arrangement described using electrolyte D from synthesis example 4 at 60° C. The current densities used were varied between 0.52 A/dm² and 10.4 A/dm². The anodic current yield up to a current density of 1.2 A/dm² or a charge density of 23.7 C/dm² is 100%. When these limit values are exceeded the erosion of the foil remains constant at 7.5±0.6 mg/dm², i.e. the anodic current yield drops constantly above the limit values. The application/deposition reaction was carried out immediately after the erosion reaction. Here too, the current densities were varied between 0.52 A/dm² and 10.4 A/dm².

The inert electrodes were provided with an anode bag before the first flowing over of the electrolyte, in order to keep the tin particles breaking off cathodically to anodically during the pole reversal of these electrodes away from the electrolyte.

After passing through the electrolysis apparatus the surface-modified foil was subjected to an after-treatment which comprised the following steps in the stated sequence:

-   -   Rinse: Water     -   Passivation: Solution of 6 g of potassium dichromate in water at         room temperature.     -   Rinse: Water     -   Drying with hot air at between 90° C. and 120° C.

TABLE 1 Results of the electrolytic treatment of a tin-plated copper foil with tin-diphosphonate electrolyte: for classification of the results the theoretical values of the deposition output for tin are given: tin(II) → tin(0) = 0.615 mg/As; tin(IV) → tin(0) = 0.308 mg/As. Current Charge Application Effective density density in output charge Serial no. A/dm² C/dm² = As/dm² in mg/As number of tin 1 0.52 2.6 0.600 2 2 0.52 5.2 0.604 2 3 0.52 10.4 0.611 2 4 1.2 6 0.608 2 5 1.2 12 0.612 2 6 1.2 24 0.605 2 7 1.77 8.85 0.594 2.07 8 1.77 17.7 0.603 2 9 1.77 35.4 0.610 2 10 3.54 17.7 0.578 2.13 11 3.54 35.4 0.591 2.08 12 3.54 70.8 0.547 2.25 13 5.82 29.1 0.561 2.19 14 5.82 58.2 0.540 2.28 15 5.82 116.4 0.536 2.30 16 8.32 41.6 0.498 2.47 17 8.32 83.2 0.471 2.61 18 8.32 166.4 0.469 2.62 19 9.36 46.8 0.485 2.54 20 9.36 93.6 0.468 2.63 21 9.36 187.2 0.463 2.68 22 10.4 52 0.490 2.51 23 10.4 104 0.469 2.62 24 10.4 208 0.472 2.61

The tin layer deposited shows highly branched aggregates and achieves a growth height of >5 μm on the foil at a charge density of 208 C/dm². At charge densities of from 90 C/dm² and constantly at >116 C/dm² the tin aggregates deposited become brittle and the colour of the surface obtained changes from light grey into matt dark grey. After conclusion of the tests the electrolyte was analyzed for the content of tin(II) (iodometrically), total tin and additionally for the introduction of copper from the foil core (Sn, Cu, -ICP-OES, nitric acid):

The concentration of tin in the electrolyte dropped from 64.7 g/l to 59.3 g/l. The tin(II) content dropped from originally 14.7 g/l (22.7%) to 1.6 g/l (2.7%). At the start no copper was to be detected in the electrolyte solution, after the end of the treatment of the tin-plated copper foil 20±5 mg of Cu/I electrolyte solution was measured.

The causes of the tin loss are the entrainment into the rinse and the asymmetry of the process between erosion and deposition on this foil. Tin was furthermore found in the anode bags of the inert electrodes. The regeneration of the tin(II) from tin(IV) at the inert cathode is incomplete. This process and the deposition of metallic tin are found here. In contrast to acid tin electrolytes of the state of the art, the ratio between tin(II) and tin(IV) in the electrolyte has no effect on the quality of the tin layer deposited. The electrolyte also shows an excellent microscatter without additives, similarly to the stannate(IV) electrolyte. Acid tin(II) electrolytes are practically unusable without additives which improve microscatter.

Example 2 Modification of a Copper Foil by Deposition of Copper Aggregates on the Foil Surface According to the Closed Neutral Conductor Principle Electrolysis Arrangement

For the surface modification of a copper foil using copper-diphosphonate electrolytes a continuous foil installation operating according to the closed neutral conductor principle designed for foils and strips up to a width of 330 mm was used. The installation substantially corresponds to the installation shown in FIG. 1 and has a pay-off reel and a pay-on reel with electronic tension control. The control possibilities comprise current strength of the individual electrode segments, strip tension, strip speed and temperature of the electrolyte.

The rectifiers used originate from the company plating electronic model pe86CW-6-424-960-4 with 4 outputs. The maximum pulse current is 960 A, the maximum constant current is 424 A. The course of the current with respect to time can be defined as the pulse sequence via the associated software.

The electrolytic cell of the continuous foil installation used comprises a cathode and an anode for one-sided electrolytic deposition. The cathode and the anode are positioned parallel to the foil run and are arranged such that, when the foil passes through, the same side or surface of the metal foil is opposite first the cathode and then the anode. Furthermore, the cathode and the anode are completely surrounded by electrolyte. Although in the tests described herein only one cathode and one anode are used, in principle a plurality of different configurations can be used, for example a double cathode and a double anode for electrolytic deposition on both sides or two cathodes and anodes arranged one after the other.

Flow electrodes which comprise an electrode housing of polypropylene and a high-current titanium contact frame with a screen surface made of titanium expanded metal which is packed behind with copper balls were used as electrodes (anode and cathode) in this test. The electrode is located in an anode bag made of PP fabric. The possible flow speed is up to 20 l/min. The electrolyte is introduced into the flow electrode via an electrolyte feed, flows past the metal balls in the direction of the base of the housing of the electrode housing and is received by an electrolyte channel in the base of the electrode housing. The electrolyte then exits the electrolyte channel via a flow opening in the form of a flow lip and flows upwards past the metal mesh. In this alternative form of the continuous foil installation, after passing through the flow electrode, the electrolyte reaches the electrolysis bath and from there via an overflow a reservoir, from which the electrolyte is then pumped again into the flow electrode.

Alternatively to the above-described and flow electrode, a three-part copper sheet convection electrode can also be used. The individual electrode segments can be controlled separately via a rectifier or connected with the same polarity. The electrode is located in an anode bag of polypropylene fabric. The necessary flow is generated by means of a B2 rod pump from Lutz (in total 40 l/min, distributed over 2 electrodes).

Surface Modification With Electrolytes K, L and M

A copper foil in the hard-as-rolled structural state having a thickness of 0.035 mm and a width of 300 mm was first subjected to a pre-treatment which comprised the following steps in the stated sequence:

-   -   Degreasing: immersion pass with electrolytic assistance, 45° C.,         alkaline cleaning agent     -   Rinse: Water, immersion pass, 45° C.     -   Pickling: Sulphuric acid 4% strength in water, immersion pass,         30-35° C.     -   Rinse: Water, immersion pass, room temperature     -   Rinse: Water, immersion pass, room temperature

The copper foil pre-treated in this way was then surface-modified in the continuous foil installation described using electrolyte K, L or M (synthesis examples 11, 12 and 13) and a further electrolyte which was prepared analogously to synthesis example 11 but to which no DTO had been added. The method parameters were as follows:

Foil speed: 2 m/min Average current strength: 66 A (=27.5 A/dm²) Pulse sequence: 10 ms at 132 A, 10 ms pause Electrolyte temperature: 50±2° C. Electrode separation: 30 mm

After passing through the electrolysis apparatus the surface-modified copper foil was subjected to an after-treatment which comprised the following steps in the stated sequence:

-   -   Rinse: Water, immersion pass, room temperature     -   Rinse: Water, immersion pass, room temperature     -   Passivation: Chromium(VI)-containing solution, immersion pass,         room temperature     -   Rinse: Water, immersion pass, room temperature     -   Rinse: De-ionized water, misting off, room temperature     -   Drying with hot air 90° C.

With Electrolytes K1, L1 and M1

A copper foil with a thickness of 0.035 mm and a width of 300 mm in the hard-as-rolled structural state was first subjected to a pre-treatment which comprised the following steps in the stated sequence:

-   -   Degreasing: Immersion pass with electrolytic support, 45° C.,         alkaline cleaning agent     -   Rinse: Water, immersion pass, 45° C.     -   Pickling: Sulphuric acid 4% strength in water, immersion pass,         30-35° C.     -   Rinse: Water, immersion pass, room temperature     -   Rinse: Water, immersion pass, room temperature

The copper foil pre-treated in this way was then surface-modified in the described continuous foil installation using electrolyte K1, L1 or M1 (synthesis examples 15, 16 and 17). The method parameters were as follows:

Foil speed: 2 m/min Average current strength: 66 A (=27.5 A/dm²) Pulse sequence: 10 ms at 132 A, 10 ms pause Electrolyte temperature: 50±2° C. Electrode separation: 30 mm

After passing through the electrolysis apparatus the surface-modified copper foil was subjected to an after-treatment which comprised the following steps in the stated sequence:

-   -   Rinse: Water immersion pass, room temperature     -   Rinse: Water, immersion pass, room temperature     -   Rinse: De-ionized water, misting off, room temperature     -   Drying with hot air 90° C.

With Electrolytes K2, K3, L3 and M3

As described above for the surface modification with electrolyte K1, after corresponding pre-treatment a copper foil was treated in the continuous foil installation described using electrolyte K2, K3, L3 or M3 (synthesis examples 19, 20, 21 and 22) and subsequently subjected to the after-treatment.

In scanning electron microscope photographs of the surface (SEM external, FEI XL 30, 45° tilt angle, 15 kV AcT (acceleration voltage), SE detector, 10,000-fold magnification) the surface-modified copper foils obtained with electrolytes K, L, M, K1, L1, M1, K2, K3, L3 and M3 showed clear and uniform deposits of copper aggregates on the copper surface, regardless of whether DTO (electrolytes K, L, M) or a compound of 4,7-dithiadecanedioic acid (electrolytes K1, L1, M1, K2, K3, L3, M3) was used. No such deposits were to be observed on a copper foil treated with the copper electrolyte without addition of an additive.

Example 3 Modification of a Copper Foil by Deposition of Tin Aggregates on the Foil Surface According to the Open Neutral Conductor Principle

For the modification of a copper foil by deposition of a tin layer in the method of the open neutral conductor principle, an apparatus as shown in FIG. 2 and as discussed above in this respect is used. A 40 metre long and 200 mm wide copper foil having a thickness of about 35 μm serves as the copper foil substrate. 2-Methoxy-1-iodobenzene is used as the separating liquid. A polypropylene container having a side wall thickness of 20 mm and a capacity of about 12 l is used as the container for the continuous apparatus. The treatment liquid used for the erosion is 30 l of the copper-diphosphonate-DTO electrolyte M (from synthesis example 13) having a copper content of 17.1 g/l, a density of 1.32 g/cm³ at 25° C. and pH=9.2 at 60° C. A frame electrode of polypropylene (PP) with a Ti expanded metal window (270 mm wide and 110 mm long in the foil running direction) which is packed behind with copper balls serves as auxiliary cathode for the erosion. The PP frame is designed such that the feed of the circulated treatment liquid through the electrode frame takes place such that the copper balls, the potential-forming window and the intermediate space between the auxiliary electrode window and the foil to be treated are washed over in a targeted manner. 30 l in total of a blend of the tin-diphosphonate electrolyte D (from synthesis example 4) and the gadolinium-diphosphonate electrolyte G (from synthesis example 7) in a ratio of 80% Sn and 20% Gd, to which 5.1 g/l of 1,8-dihydroxy-3,6-dithiaoctane are added, are used as the treatment liquid for the deposition. The same electrode type as in the erosion zone is used as auxiliary anode, but instead of the copper balls tin granules having a maximum diameter of up to 12 mm are used as the packing behind the Ti expanded metal window. This treatment liquid is also used at 60° C., pH=9.2. The two treatment liquids are present in separate reservoir tanks and are circulated completely within 15 minutes in each case. The separating liquid is used as a static phase at the base of the treatment cell and is present in an amount of 4 l (=7.3 kg). The foil is passed by the electrodes at a speed of 0.4 m/min. The electrode length in the foil running direction is 110 mm. The current density used is applied in various pulses and is 6.82 A/dm². The charge density applied is 112 C/dm².

After the treatment of the copper foil the layer weight of tin/Gd deposited on the copper foil, the content of Gd with respect to tin in the layer, the metal contents of the treatment liquids and the entrainment of copper from the erosion zone into the deposition zone are determined:

Average layer weight: 1.1±0.1 g/m² Molar ratio of Gd/Sn in the layer: 68 ppm Content of copper in the erosion electrolyte: 16.9 g/l (start 17.1 g/l) Content of tin in the deposition electrolyte: 51.1 g/l (start 51.7 g/l) Content of gadolinium in the deposition electrolyte: 16.8 g/l (start 16.7 g/l) Entrained soluble copper in the deposition electrolyte: <0.02 g/l

The probe elements of the treatment liquids or of the separating agent potassium, phosphorus, sulphur and iodine are not detected in the layer deposited (<5 ppm).

Investigation of the Adhesion Properties Test Method 1—Adhesion Test

An adhesive strip (Tesafilm® Transparent 57404-00002) was placed over the electrolytically treated, dry, cold metal foil surface which had been stored for at least 15 minutes and pressed firmly onto the surface with a soft roller. Care was taken that no air bubbles formed between the adhesive tape and the foil surface. After a period of 30 seconds after the adhesive strip had been pressed on, it was gripped at its projection and pulled off from the firmly held metal foil. A pulling speed of 2 to 3 seconds for a length of 8 cm was maintained.

The pulled off adhesive strip was then stuck to a white sheet of paper and the colour change caused by metal aggregates which are torn off from the foil surface and remain on the adhesive strip was assessed. Furthermore, it was assessed whether the adhesive layer of the Tesafilm remained either totally or partially on the surface of the metal foil after the pulling off.

Test Method 2—Peel Strength Test

The peel strength was determined in accordance with DIN EN 60249 on a Zwick BZ2/TN1S model peel device with an Xforce HP 500 N load cell and testXpert 12.3 software. For this, the samples were cut out of a pressed composite sheet and the foil was pulled off or peeled off at an angle of 180°. The pressed composite sheet was produced by pressing the foil with a plastic substrate at a temperature of 160±10° C. under a pressing pressure of 120±5 bar over a period of 60±5 min. The results of the peel test are given in N/mm.

Example 4 Adhesion to Tin-Plated Copper Foil Treated with Tin-Diphosphonate Electrolyte

The foils obtained in Example 1 with tin growths which were not brittle (serial no. 1 to 14, see Table 1) were subjected to the adhesion test described above. Conventionally produced, non-passivated and non-oiled tinplate surfaces in the original (dendritic) deposition state and in the melted down state (application of 8.2 g of Sn/m² of surface, 0.32 mm core strip, unstructured (Giebel KWVV GmbH Iserlohn)) served for comparison. All the samples showed a significantly improved adhesive strength of the adhesive strip on the metal surface coated with tin compared with the tinplate surface, which manifested itself as greying of the foil adhesive layer due to torn-off tin aggregates. Samples 4-14 no longer allow a simple pulling off of the adhesive strip; the adhesive layer remains stuck in the surface of the foil, and in particular cases the foil tears when pulled off. In contrast, the tinplate surfaces used for comparison purposes allow complete pulling off of the adhesive strip in all cases. Pulling off of the adhesive strip from the surface of the tinplate in the melted down state takes place to the extent of 80% without leaving behind visible traces on the surface.

Example 5 Adhesion to Copper Foil Surface-Modified with Copper-Diphosphonate-Additive Electrolyte

The adhesion test described above and in Example 4 was repeated with the copper foils obtained in Example 2 surface-modified with electrolytes K1, L1, M1 (additive=DTDA), K2 (additive=DMDTK) or K3, L3, M3 (additive=DMDTDA). The tests resulted in an outstanding adhesion of the adhesive film on the copper layer. In all the tests the adhesive film adhered over the complete area, and on pulling off the adhesive film the adhesive layer of the film remained on the copper layer.

The surface modification of copper foils using copper-diphosphonate electrolytes with the addition of additive, for example in the closed neutral conductor principle, thus delivers strongly adhering surfaces which have, inter alia, outstanding adhesive strengths with respect to adhesive tape.

Example 6 Adhesion to Copper Foil Treated with Tin-Diphosphonate Electrolyte

The adhesion test described above and in Example 4 was repeated with the copper foil obtained in Example 3 Sn-modified in the method according to the open neutral conductor principle. The test resulted in an outstanding adhesion of the adhesive film on the tin layer. The adhesive layer of the film remained on the tin layer, or the film strip was destroyed in the test of pulling off from the tin surface.

The use of tin-diphosphonate electrolytes for deposition of Sn layers thus delivers microstructured, strongly adhering surfaces which have inter alia outstanding adhesive strengths with respect to adhesive tape both in the closed and in the open neutral conductor principle in the deposition process.

Example 7 Peel Strengths of Pressed Composite Sheets of Copper Foils Modified with Copper-DTO Electrolyte and Various Plastics

Composite sheets were produced by pressing the copper foil of Example 2 surface-modified with electrolyte L and the following plastic substrates: a) Ultramid® A3X2 G5, b) Grivory® HT2V-3H, c) FR-4 epoxy resin and d) FR-4 polyimide. A composite sheet which was produced from copper foil (analogous to Example 2) electrolytically modified with the electrolyte without DTO addition (electrolyte 0: copper content 7.0 g/l, sulphate content 69.4 g/l, density 1.07 g/cm³) and FR-4 epoxy resin served for comparison. The peel strengths of the respective composite sheets were investigated in accordance with the peel strength test described above and are:

Electrolyte L/Ultramid ® A3X2 G5 1.7 N/mm Electrolyte L/Grivory ® HT2V-3H 1.3 N/mm Electrolyte L/FR-4 epoxy resin 2.0 N/mm Electrolyte L/FR-4 polyimide 1.7 N/mm Electrolyte 0/FR-4 epoxy resin 1.2 N/mm

In FIG. 4 the peel strengths are shown on a graph for better illustration. As can be seen from these data, the peel strength of a composite of FR-4 epoxy resin and copper foil modified with electrolyte L increases significantly compared with that of a composite of FR-4 epoxy resin and copper foil modified with electrolyte 0. The peel tests with the plastic substrates also demonstrate the outstanding adhesive potential of the surfaces modified according to the invention. 

1-21. (canceled)
 22. Electrically conductive liquid comprising an aqueous solution of a metal complex, wherein the metal complex is a complex of (i) one or more metals selected from the group consisting of Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co, Ti, Zr, Nb, Y, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof, and (ii) one or more diphosphonate ligands of the general formula (I) O═P(OH)₂—X—(OH)₂P═O  (I) wherein: X=O, NR¹ or CR¹R², R¹=H, C₁-C₁₈-n-alkyl or C₃-C₁₈-isoalkyl, C_(s)-C₆-cycloalkyl, unsubstituted or substituted benzyl and substituted or unsubstituted phenyl, R²=R¹, —OR³ or —NHR³, and R³=H, C₁-C₄-n-alkyl or C₃-C₄-isoalkyl, and wherein the OH groups in the general formula (I) which are bonded to the two phosphorus atoms independently of each other are protonated (OH) or deprotonated (O⁻), wherein the liquid furthermore optionally comprises an additive of the general formula (II): R¹⁰—CHR⁸—CHR⁹—Z—(CHR⁴—CHR⁵—Z)_(n)—CHR⁶—CHR⁷—R¹⁰  (II) wherein: n=an integer from 1 to 11, Z=S or O, R⁴=H, C₁₋₄-alkyl or phenyl, R⁵=H, C₁₋₄-alkyl or phenyl, R⁶=H, C₁₋₄-alkyl or phenyl, R⁷=H, C₁₋₄-alkyl or phenyl, R⁸=H, C₁₋₄-alkyl or phenyl, R⁹=H, C₁₋₄-alkyl or phenyl, R¹⁰=OH, COOH or COOR¹¹ and R¹¹=C₁₋₄-alkyl, Li, Na, or K.
 23. The liquid according to claim 22 wherein X=CR¹R².
 24. The liquid according to claim 22 wherein Z is S.
 25. The liquid according to claim 22 wherein n is 1, 2, or
 3. 26. The liquid according to claim 22, wherein the metal is Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co, Ti, Zr, Nb, or mixtures thereof, said metal being optionally doped with Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or mixtures thereof.
 27. The liquid according to claim 26 wherein the metal is Cu.
 28. The liquid according to claim 26, wherein the metal is Fe, Ni, Co or mixtures thereof, wherein the metal is doped with Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or mixtures thereof.
 29. The liquid according to claim 28 wherein the metal is doped with Sm, Gd, Dy, Er or mixtures thereof.
 30. The liquid according to claim 22, wherein the additive is present in an amount of 1 wt % or less based on the weight of the total solution.
 31. The liquid according to claim 30, wherein the additive is present in an amount ranging from 0.05 to 0.7 wt %, based on the weight of the total solution.
 32. The liquid according to claim 30, wherein the additive is present in an amount ranging from 0.1 to 0.5 wt %, based on the weight of the total solution.
 33. The liquid according to claim 1, wherein the liquid comprises an additive of the formula (II), wherein n=an integer from 1 to 3, Z=S, R⁴=H, methyl, ethyl, n-propyl or n-butyl, R⁵=H, methyl, ethyl, n-propyl or n-butyl, R⁶=H, methyl, ethyl, n-propyl or n-butyl, R⁷=H, methyl, ethyl, n-propyl or n-butyl, R⁸=H, methyl, ethyl, n-propyl or n-butyl, R⁹=H, methyl, ethyl, n-propyl or n-butyl, R¹⁰=OH, COOH or COOR¹¹, and R¹¹=K, methyl, ethyl or n-propyl.
 34. The liquid according to claim 33, wherein the additive is 1,8-dihydroxy-3,6-dithiaoctane.
 35. The liquid according to claim 22, wherein the metal is Cu and the additive is 1,8-dihydroxy-3,6-dithiaoctane.
 36. The liquid according to claim 22, wherein the liquid is substantially free from sulphate, nitrate, halogenate and halide ions.
 37. The liquid according to claim 22, wherein the liquid comprises no additional buffer in addition to the ligand of the formula (I).
 38. A method for the electrolytic surface modification of a flat metal workpiece, comprising: (a) anodically polarizing at least one surface of the flat metal workpiece in a treatment liquid, whereby an anodic dissolving process is thereby induced, and then (b) cathodically polarizing said at least one surface of the flat metal workpiece in a treatment liquid, whereby a cathodic deposition process is thereby induced for the deposition of one or more metals on the at least one surface of the flat metal workpiece, said treatment liquid being a liquid according to claim
 22. 39. The method according to claim 38, wherein the flat metal workpiece is anodically polarized by at least one cathode without direct contacting for the induction of the dissolving process, the flat metal workpiece is cathodically polarized by at least one anode without direct contacting for the induction of the deposition process, and the cathode and the anode are arranged in such a way that treatment liquid is located between anode and metal workpiece and between cathode and metal workpiece.
 40. The method according to claim 38, wherein the treatment liquid in the anodic dissolving process and the treatment liquid in the cathodic deposition process are different treatment liquids and the treatment liquid in the anodic dissolving process and the treatment liquid in the cathodic deposition process are separated by a non-conductive separating liquid which has contact to the flat metal workpiece.
 41. The method according to claim 38, wherein layers of host metals doped with doping metals are deposited by varying the average current density of the deposition and the concentration ratio between the doping metal(s) and host metal(s) between 1:5 and 150:1 in the treatment liquid, wherein the host metals are selected from Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co and mixtures thereof, and the doping metals are selected from Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ti, Zr, Nb or mixtures thereof, and are present in the layer in an amount ranging from 1 ppm to 20,000 ppm.
 42. The method according to claim 38, wherein ferromagnetic closed layers of the metals Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co, Nb or mixtures thereof which are doped with Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or mixtures thereof are deposited in a thickness ranging from 10 nm to 1 μm and have a greater layer thickness of the changeover between the in-plane and the out-of-plane orientation of the domains than in the case of ferromagnetic, pure metal layers deposited by vacuum.
 43. The method according to claim 38, wherein corrosion-stable iron and/or tin surfaces and recrystallization-inhibited tin surfaces are produced.
 44. A flat metal workpiece obtained from the method according to claim
 38. 45. A flat metal workpiece having a surface which comprises uniformly distributed discrete metal aggregates which protrude therefrom, wherein 90% or more of the metal aggregates have a size ranging from 0.05 to 1 μm, said metal aggregates being comprised of metals selected from Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co, Nb and mixtures thereof, said surface having an average roughness values Ra and Rz values, as determined in accordance with DIN EN ISO 4288:1998, range from 0.22 to 0.32 μm and 1.4 to 2.1 μm, respectively.
 46. The flat metal workpiece according to claim 45 wherein the metals are doped with one or more doping metal(s) selected from Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ti, Zr and mixtures thereof, and the doping metal(s) is (are) present in the metal aggregate in an amount ranging from 1 ppm to 20,000 ppm.
 47. The flat metal workpiece according to claim 45, wherein the surface of the flat metal workpiece comprises metal aggregates, wherein 90% or more of the metal aggregates have a size ranging from 0.3 to 0.7 μm.
 48. The flat metal workpiece according to claim 47, wherein the surface of the flat metal workpiece comprises metal aggregates, wherein 90% or more of the metal aggregates have a size ranging from 0.35 to 0.65 μm.
 49. The flat metal workpiece according to claim 48, wherein the surface of the flat metal workpiece comprises metal aggregates, wherein 99% or more of the metal aggregates have a size ranging from 0.3 to 0.7 μm.
 50. The flat metal workpiece according to claim 44, wherein the surface of the flat metal workpiece is comprised of metal aggregates, wherein the metal aggregates are comprised of Cu, Zn, Mn, In, Sn, Sb, Bi, Fe, Ni, Co, Nb or mixtures thereof.
 51. A composition of matter comprised of the flat metal workpiece of claim
 44. 52. A composition of matter comprised of the flat metal workpiece of claim
 45. 53. The composition of matter of claim 52 bonded to materials selected from thermoplastics, synthetic resins, adhesives, lacquers and pastes.
 54. The flat metal workpiece according to claim 45 comprised of a metal selected from copper, tin, zinc, aluminium, iron and nickel or a metal alloy comprised of copper, iron, silver or tin.
 55. The flat metal workpiece according to claim 45 comprised of copper upon which copper aggregates are deposited on the surface thereof.
 56. The flat metal workpiece according to claim 45 wherein the average roughness values Ra and Rz range from 0.24 to 0.28 μm and from 1.6 to 1.9 μm, respectively. 